Astronomy of To-day

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					The Project Gutenberg EBook of Astronomy of To-day, by Cecil G. Dolmage




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Title: Astronomy of To-day

   A Popular Introduction in Non-Technical Language

Author: Cecil G. Dolmage

Release Date: April 21, 2009 [EBook #28570]

Language: English

Character set encoding: ISO-8859-1

Produced by Brenda Lewis, Scott Marusak, Greg Bergquist


generously made available by The Internet Archive/American


*Transcriber?s Note*

The punctuation and spelling from the original text have been faithfully

preserved. Only obvious typographical errors have been corrected. The

advertisement from the beginning of the book has been joined with the

other advertisements near the end of the book.




The Total Eclipse of the Sun of August 30th, 1905. The Total Eclipse of

the Sun of August 30th, 1905.

The Corona; from a water-colour sketch, made at Burgos, in Spain, during

the total phase, by the French Artist, Mdlle. Andrée Moch.








Fellow of the Royal Astronomical Society; Member of

the British Astronomical Association; Member of

the Astronomical Society of the Pacific; Membre

de la Société Astronomique de France;

Membre de la Société Belge

With a Frontispiece in Colour

and 45 Illustrations & Diagrams




38 Great Russell Street






the /general reader/.

knowledge of Astronomy without much laborious study, and without




mathematics is perhaps responsible for the idea that some kind of


more than ordinary logic in concentrated form, the /shorthand of

reasoning/, so to speak. I have attempted in the following pages to take

the main facts and theories of Astronomy out of those mathematical forms

which repel the general reader, and to present them in the /ordinary

language of our workaday world/.

The few diagrams introduced are altogether supplementary, and are not



case the wording of the text should not have perfectly conveyed the

desired meaning. The full page illustrations are also described as

adequately as possible at the foot of each.


itself. It is the work of the /artist/ as distinct from the scientist.

The book itself contains incidentally a good deal of matter concerned

necessary in order to make clearer the Astronomy of our time.


from which information has been drawn. But I acknowledge my especial

indebtedness to Professor F.R. Moulton's /Introduction to Astronomy/


Johnson and of Mr. W.T. Lynn, and to the excellent /Journals of the

British Astronomical Association/. Further, for those grand questions


the writings of the famous American astronomer, Professor Simon Newcomb,


am under an additional obligation for much valuable information

privately rendered.





thanks as follows:?To the French Artist, Mdlle. Andrée Moch; to the






publishers of /Knowledge/, and to Messrs. Sampson, Low & Co. For

permission to reproduce the beautiful photograph of the Spiral Nebula in

Canes Venatici (Plate XXII. <#Plate_XXII>), I am indebted to the





Cambridge, for their kindness in reading the proof-sheets.


London, S.W.,

/August 4, 1908./






of the second edition which it has so soon reached.

/December 1908./




The Ancient View                17


The Modern View                 20


The Solar System                29


Celestial Mechanism             38


Celestial Distances             46


Celestial Measurement 55


Eclipses and Kindred Phenomena                       61


Famous Eclipses of the Sun                83


Famous Eclipses of the Moon               101

The Growth of Observation      105


Spectrum Analysis      121


The Sun         127


The Sun?/continued/    134


The Inferior Planets   146


The Earth       158


The Moon        183


The Superior Planets   209


The Superior Planets?/continued/     229


Comets          247


Remarkable Comets      259


Meteors Or Shooting Stars      266

The Stars            278


The Stars?/continued/ 287


Systems of Stars                300


The Stellar Universe            319


The Stellar Universe?/continued/                     329


The Beginning of Things                   333


The End of Things               342

Index <#INDEX>                  351





          The Total Eclipse of the Sun of August 30, 1905                  /Frontispiece/

I. <#Plate_I>    The Total Eclipse of the Sun of May 17, 1882    /To face

page/ 96

II. <#Plate_II> Great Telescope of Hevelius       " "      110

III. <#Plate_III> A Tubeless, or "Aerial" Telescope        " "   112

IV. <#Plate_IV> The Great Yerkes Telescope        " "      118

V. <#Plate_V> The Sun, showing several groups of Spots           " "    134

VI. <#Plate_VI> Photograph of a Sunspot           " "      136

VII. <#Plate_VII>        Forms of the Solar Corona at the epochs of Sunspot


and Sunspot Minimum respectively.

(/A/) The Total Eclipse of the Sun of December 22, 1870.

(/B/) The Total Eclipse of the Sun of May 28, 1900         " "   142

VIII. <#Plate_VIII>      The Moon        " "      196

IX. <#Plate_IX> Map of the Moon, showing the principal "Craters," Mountain

Ranges And "Seas"        " "     198

X. <#Plate_X> One of the most interesting Regions on the Moon           " "   200

XI. <#Plate_XI> The Moon (showing systems of "Rays") " "         204

XII. <#Plate_XII>        A Map of the Planet Mars          " "   216

XIII. <#Plate_XIII>      Minor Planet Trails      " "      226

XIV. <#Plate_XIV>        The Planet Jupiter       " "      230

XV. <#Plate_XV>          The Planet Saturn        " "      236

XVI. <#Plate_XVI>        Early Representations of Saturn " "     242

XVII. <#Plate_XVII>      Donati's Comet " "       256
XVIII. <#Plate_XVIII>           Daniel's Comet of 1907 " "                 258

XIX. <#Plate_XIX>               The Sky around the North Pole " "                292

XX. <#Plate_XX>                 Orion and his Neighbours                   " "   296

XXI. <#Plate_XXI>               The Great Globular Cluster in the Southern Constellation

of Centaurus         " "        306

XXII. <#Plate_XXII>             Spiral Nebula in the Constellation of Canes

Venatici             " "        314

XXIII. <#Plate_XXIII>           The Great Nebula in the Constellation of

Andromeda            " "        316

XXIV. <#Plate_XXIV>             The Great Nebula in the Constellation of Orion

" "       318



FIG.                 PAGE

1. <#Fig_1>          The Ptolemaic Idea of the Universe                    19

2. <#Fig_2>          The Copernican Theory of the Solar System                   21

3. <#Fig_3>          Total and Partial Eclipses of the Moon 64

4. <#Fig_4>          Total and Partial Eclipses of the Sun                 67

5. <#Fig_5>          "Baily's Beads" 70

6. <#Fig_6>          Map of the World on Mercator's Projection, showing a

portion of the progress of the Total Solar Eclipse Of August 30, 1905,
across the surface of the Earth 81

7. <#Fig_7>          The "Ring with Wings" 87

8. <#Fig_8>          The Various Types of Telescope 113

9. <#Fig_9>          The Solar Spectrum              123

10. <#Fig_10> A Section through the Sun, showing how the Prominences

rise from the Chromosphere                131

11. <#Fig_11> Orbit and Phases of an Inferior Planet                       148

12. <#Fig_12> The "Black Drop"                       153

13. <#Fig_13> Summer and Winter                      176

14. <#Fig_14> Orbit and Phases of the Moon 184

15. <#Fig_15> The Rotation of the Moon on her Axis                         187

16. <#Fig_16> Laplace's "Perennial Full Moon"                              191

17. <#Fig_17> Illustrating the Author's explanation of the apparent

Enlargement of Celestial Objects                     195

18. <#Fig_18> Showing how the Tail of a Comet is directed away from the

Sun       248

19. <#Fig_19> The Comet of 1066, as represented in the Bayeux

Tapestry             263

20. <#Fig_20> Passage of the Earth through the thickest portion of a

Meteor Swarm 269


[Pg 17]





perhaps more true of astronomy than of anything else.












heaven from falling in upon men and crushing them out of existence?[Pg

18] Fantastic myths sprang from the vain attempts to solve these





punishment for revolt against the Olympian gods, was condemned to hold

up the expanse of sky for ever and ever.


Greek philosophers, who busied themselves much with such matters,

gradually became convinced that the earth was spherical in shape, that






philosophers had become hardened into a definite theory, which, though


notice from the fact that it was everywhere accepted as the true



astronomers of antiquity, Claudius Ptolemæus Pelusinensis (100?170

A.D.), better known as Ptolemy of Alexandria.



then the planets Mars, Jupiter, and Saturn. Beyond[Pg 19] these again


the stars were fixed?

"Stellis ardentibus aptum,"

as Virgil puts it (see Fig. 1 <#Fig_1>).

Fig. 1. Fig. 1.?The Ptolemaic idea of the Universe.

The Ptolemaic system persisted unshaken for about fourteen hundred years




things revolved.


[Pg 20]



Copernican, theory of the universe supplanted the Ptolemaic, which had


towards the middle of the sixteenth century by Nicholas Copernicus

(1473?1543), a Prussian astronomer, the earth was dethroned from its

central position and considered merely as one of a number of planetary




accepted and believed in to-day.






(see Fig. 2 <#Fig_2>, p. 21). At an immense distance beyond the solar




The remaining members (exclusive of the earth) are called Superior


[Pg 21]

Fig. 2. Fig. 2.?The Copernican theory of the Solar System.

[Pg 22]



strongly the immense advance which has taken place in astronomy during




constellation of the Twins, that the justly famous Sir William Herschel






its discovery the hitherto accepted limits of the solar system were at

arose that other planets would quickly reveal themselves in the

immensities beyond.


noticed that the distances at which the then known planets circulated

appeared to be arranged in a somewhat orderly progression outwards from


Law, was[Pg 23] closely confirmed by the distance of the new planet





reasonably expect to find another planet circling was unaccountably empty.

On the first day of the nineteenth century the mystery was however

explained, a body being discovered[1] <#Footnote_1_1> which revolved in










known to exist, all revolving in the previously unfilled space between

Mars and Jupiter.


extended by the discovery that a great planet circulated beyond Uranus.

The new body, which received the name of Neptune, was[Pg 24] brought to


independently, by the Cambridge mathematician Adams, and the French



course of ordinary telescopic survey of the heavens. The position of


mathematical investigations undertaken with the object of fixing the



revolution around the sun. Adams actually completed his investigation





Verrier had mathematically predicted for it.

important planetary discovery was made. One of the recent additions to

the numerous and constantly increasing family of the asteroids, a tiny


circulating in the customary space between Mars and Jupiter, but




size as compared with the other leading members of the system.

This completes the list of the planets which, so[Pg 25] far, have






"discovered" in 1859 by a French doctor named Lescarbault, of Orgères


evidence of its existence. The reason why such uncertainty should exist


overpowering glare which fills our atmosphere all around the sun's place







circulates within the path followed by Mercury. The opportunity in






the sun have, however, come and gone since the days of Lescarbault,[Pg

26] and no planet, so far, has revealed itself in the intra-Mercurial


sufficient size to be seen by means of our modern telescopes circulates

nearer to the sun than the planet Mercury.



of Satellites. The name /satellite/ is derived from a Latin word

signifying /an attendant/; for the bodies so-called move along always in


they accompany are technically termed.

The satellites cannot be considered as allotted with any particular

regularity among the various members of the system; several of the

planets, for instance, having a goodly number of these bodies







present know, Jupiter possesses seven,[2] <#Footnote_2_2> Saturn ten,



number of these secondary bodies revolving around them; but,

unfortunately, the Uranian and[Pg 27] Neptunian systems are at such

immense distances from us, that even the magnificent telescopes of

to-day can extract very little information concerning them.









turned his newly invented telescope upon Jupiter, he quickly recognised

the solar system.



Meteors. Comets differ from the bodies which we have just been

describing in that they appear filmy and transparent, whereas the others


of the satellites around their primaries are not actually circles; they


comets on the other hand are usually /very/ oval; so that in their



tendency is to consider comets as permanent members of the system,

though[Pg 28] this was formerly not by any means an article of faith

with astronomers.





the friction of rushing through the atmosphere, and are thus usually


globe. Though occasionally a meteoric body survives the fiery ordeal,


in the soil, the majority of these celestial visitants constitute no







[1] <#FNanchor_1_1> By the Italian astronomer, Piazzi, at Palermo.

[2] <#FNanchor_2_2> Probably eight. (See note, page 232. <#Page_232>)


[Pg 29]




is composed as follows:?there is a central body, the sun, around which

revolve along stated paths a number of important bodies known as

company still smaller bodies called satellites, which revolve around





and the satellites.


which appears to characterise all solid objects in the celestial spaces:

they are spherical, which means /round like a ball/.




follows:?Imagine a ball with a knitting-needle run right through its

centre. Then imagine this needle held pointing in one fixed direction

while the ball is turned round and round. Well, it is the same[Pg 30]


round and round continually as if pivoted upon a mighty knitting needle


is no such material axis to regulate the constant direction of the



which control their motions, are far more wonderful than any mechanical

At this juncture it will be well to emphasise the sharp distinction

between the terms /rotation/ and /revolution/. The term "rotation" is

invariably used by astronomers to signify the motion which a celestial



earth, for instance, we say, that it /rotates/ on its axis, and that it

/revolves/ around the sun.





planets and satellites of the system rolled together. Next comes Jupiter

and afterwards the other planets in the following order of size:?Saturn,




the zone of asteroids should mark the separation of the small planets

from the giant[Pg 31] ones. The following table, giving roughly the


clearly illustrate the great discrepancy in size which prevails in the

Sun     866,540          miles

Mercury          2,765 "

Venus 7,826 "

Earth   7,918 "

Mars    4,332 "


Jupiter 87,380 "

Saturn 73,125 "

Uranus[3] <#Footnote_3_3>         34,900 "

Neptune[3] <#Footnote_3_3> 32,900 "








Next with respect to relative distance from the sun, Venus circulates


far, and[Pg 32] Mars nearly four times. After this, just as we found a



and Neptune about seventy-seven. (See Fig. 2 <#Fig_2>, p. 21.)








supposed boundary of our solar system prior to the year 1781.

We have seen that the usual shape of celestial bodies themselves is

spherical. Of what form then are their paths, or /orbits/, as these are





not by any means of the same degree. Some orbits?for instance, that of

the earth?differ only slightly from circles; while others?those of Mars

or Mercury, for example?are markedly elliptic. The orbit of the tiny



It has been stated that the sun and planets are[Pg 33] always rotating.



that the earth rotates at all?





as the /Pole Star/. This was one of the earliest facts noted with regard





any knowledge of the kind they were inclined to imagine them

comparatively near. It was indeed only after the lapse of many

centuries, when men had at last realised the enormous gulf which


reasonable opinion began to prevail. It was then seen that this


satisfactorily explained by supposing a mere rotation of the solid earth



further strengthened by the observations made with the telescope. When

the surfaces of the sun and planets were carefully studied these bodies
were seen to be rotating. This[Pg 34] being the case, there could not

surely be much hesitation in granting that the earth rotated also;


and saved men from the almost inconceivable notion that the whole

stupendous vaulted heaven was turning about them once in every

twenty-four hours.


be gathered from the slow displacement of sunspots across its face,

their disappearance at one edge and their reappearance again at the







as these planets are at such great distances that even our best




the neighbourhood of Mercury and Venus equally hampers astronomers in

this quest. The older telescopic observers considered that the rotation




referred[Pg 35] to later on; but, putting it on one side, it will be




/days/ need not seem extraordinary when one considers its enormous size.




how the periods taken by the other planets compare with it.

The earth takes about 365¼ days to revolve around the sun. This period



complete revolution round the sun:?

Mercury          about 88         days.

Venus "          226        "

Mars    "        1        year and 321 days.

Jupiter "        11       years and 313 days.

Saturn "         29       years and 167 days.

Uranus "         84       years and 7 days.

Neptune          "        164     years and 284 days.

a planet is to the sun the faster it revolves.



Neptune about the middle of the reign of George II., that "year"[Pg 36]



Uranus, too, has only completed a little more than 1½ of its "years"

since Herschel discovered it.


the next point to be inquired into is:?What are the positions of their

orbits, or paths, relatively to each other?





condition of things?




would be described in astronomical parlance as being /in the same

plane/. Suppose, on the other hand, that some of these floating hoops


out of the water and the other half consequently sinks beneath the



one of them is tilted, or /inclined/, a little with respect to the plane


/level/ of the solar system. This tilting, or "inclination," is, in the

larger planets, greatest for the orbit of Mercury,[Pg 37] least for that


of about 7°, that of Venus at a little over 3°, that of Saturn 2½°;


than 2°. But greater than any of these is the inclination of the orbit

of the tiny planet Eros, viz. nearly 11°.

The systems of satellites revolving around their respective planets


solar system, the considerations so far detailed, which regulate the





whereas the planetary body around which a satellite revolves is not.




system and a satellite system is remarkable. The satellites are





all the satellites revolve around their primaries at rates which are

directly comparable with those at which the planets revolve around the


primary the faster it revolves.

[3] <#FNanchor_3_3> As there seems to be much difference of opinion

concerning the diameters of Uranus and Neptune, it should here be

mentioned that the above figures are taken from Professor F.R. Moulton's

/Introduction to Astronomy/ (1906). They are there stated to be given on



[Pg 38]



various members of the solar system we are struck with a certain



estimates of them either as regards /volume/?that is to say, the mere

room which they take up; or as regards /mass/?that is to say, the amount

of matter which they contain.




greater /density/, as the term goes. That globe is said to be the





it had the greater mass.



beginning with the greatest:?the Sun, Jupiter, Saturn,[Pg 39] Uranus,
Neptune, the Earth, Venus, Mars, and Mercury.








little greater than that of water.










less dense.


/Gravitation/, or /gravity/, as it is often called, is the attractive



so of their own accord, as if it[Pg 40] were quite natural, or rather


















limp, and the stone will fall back towards our hand.





regulated that these pulls exactly balance each other, the stone travels

comfortably round and round, and shows no tendency[Pg 41] either to fall






tend to rush away into space.










distance, controlling perhaps, in their courses, unseen planets circling


force of gravity acts depends upon distance in a regularly diminishing






earth. Last of all,[Pg 42] the point in a body from which the attraction


rather what is known as its /centre of gravity/, that is to say, the

balancing point of all the matter which the body contains.



orbs revolve around their /common/ centre of gravity, which is a point




within the body of the sun.


satellites around their respective planets, will therefore be readily

understood to result from a nice balance between gravitation and speed

of motion.


comparing the revolutions of its satellite or satellites around it, with







With regard, however, to Venus and Mercury, the problem is by[Pg 43] no


information in this latter case we have to rely upon such uncertain




happen to pass near to them.




entirely upon the gravitational pull which it receives. The force of






be seen that if a body of given /mass/ were to be placed upon planet
after planet in turn, its /weight/ would regularly alter according to

the force of gravity at each planet's surface.




answer. Its action across space appears to be instantaneous.

The intensity of gravitation is said in mathematical parlance "to vary

inversely with the square of the distance." This means that at /twice/

the distance the[Pg 44] pull will become only /one-quarter/ as strong,

and not one-half as otherwise might be expected. At /four/ times the

distance, therefore, it will be /one-sixteenth/ as strong. At the


as we ordinarily term it, through 16 feet in one /second/ of time;


very much weakened that a body would take as long as one /minute/ to

fall through the same space.

Newton's investigations showed that if a body were to be placed /at

rest/ in space entirely away from the attraction of any other body it

would remain always in a motionless condition, because there would




gravitational attraction of any other body.

The possibility of an interaction between the celestial orbs had





/emanation/ from the earth. But no one prior to Newton attempted to

examine the question from a mathematical standpoint.

Notwithstanding the acknowledged truth and far-reaching scope of the law

of gravitation?for we find its effects exemplified in every portion of

the universe?there[Pg 45] are yet some minor movements which it does not

account for. For instance, there are small irregularities in the

movement of Mercury which cannot be explained by the influence of

possible intra-Mercurial planets, and similarly there are slight

unaccountable deviations in the motions of our neighbour the Moon.


[Pg 46]


Up to this we have merely taken a general view of the solar system?a

bird's-eye view, so to speak, from space.

In the course of our inquiry we noted in a rough way the /relative/


not yet stated what these distances /actually/ are, and it were

therefore well now to turn our attention to this important matter.



lies such and such a number of miles away.

The measurements which have already been given of the diameters of the




various planets revolve in their orbits.

The following table gives these distances in round numbers. As here


oval, the planets vary in their distances from the sun, and[Pg 47] we
are therefore obliged to strike a kind of average for each case:?

Mercury         about 36,000,000          miles.

Venus "         67,200,000       "

Earth   "       92,900,000       "

Mars    "       141,500,000      "

Jupiter "       483,300,000      "

Saturn "        886,000,000      "

Uranus "        1,781,900,000 "

Neptune         "        2,791,600,000 "


still greater scale of distance than in dealing with the diameters of






we are ordinarily accustomed?the few miles' walk, the little stretch of

sea or land which we gaze upon around us?are so utterly minute in






such[Pg 48] as one can take in with a glance; but in our estimation of a


trick, so to speak.






which an express train travels.














take about 178 /years/ to traverse this.

Having arrived at the sun, let us suppose that our[Pg 49] train makes a





traverse the distance.




space appalling to contemplate, when one realises that a body moving






Having thus concluded our general survey of the appearance and


and size in relation to what we call the Universe.




light is quite overpowered by the dazzling light of the sun.


fact, lies plunged within the midst[Pg 50] of a great tangle of stars.


the centre, or anywhere near the centre, or where?

It has been indeed amply proved by astronomical research that the stars






meteors;?or perchance indeed some further variety of attendant bodies of






deduction that as the stars have characteristics similar to our








and we can gaze between them out into the blackness of the void[Pg 51]

which, perhaps, continues to extend unceasingly long after the very




express-train method of gauging space would fail miserably in the







historical time in a journey from the sun to Neptune.










million is itself a million. Here is a way of trying to realise this[Pg

52] gigantic number. A million seconds make only eleven and a half days


thousand years!




billion miles?that is to say, a million times this distance?would thus




This shows how useless our illustration, appropriate though it seemed

for interplanetary space, becomes when applied to the interstellar





the velocity of light.







separates us from Alpha Centauri[Pg 53] it would take so long as about

four and a quarter years!

Astronomers, therefore, agree in estimating the distances of the stars





distant from us.







already started upon their journey towards our earth must indeed


had arrived; after which no more would come.









Pyramids[Pg 54] of Egypt were being built? Even the last of these

suppositions cannot be treated lightly. We have indeed no real knowledge


brought into view out of the depths of the celestial spaces.


[Pg 55]


Had the telescope never been invented our knowledge of astronomy would

be trifling indeed.











particular characteristics to distinguish them from the great host of

the stars, except that they continually changed their positions in the



apparently moved about in the intermediate space, supported in their

yet unknown. Comets were regarded as[Pg 56] celestial portents, and

meteors as small conflagrations taking place in the upper air.


and distances of the various celestial bodies, men naturally considered


assigned to them in consequence a permanent connection with terrestrial

affairs. Thus arose the quaint and erroneous beliefs of astrology,

according to which the events which took place upon our earth were

considered to depend upon the various positions in which the planets,

for instance, found themselves from time to time.


fallacious though its conclusions were, indirectly performed a great

service to astronomy by reason of the accurate observations and diligent

study of the stars which it entailed.



ancients were so entirely in the dark in this matter.


object happens to be situated from us.

One method is by actual measurement.

observing whether the distant object appears in any degree altered in

position by our own change of place.

One of the best illustrations of this relative change of position which


the landscape from the[Pg 57] window of a moving railway carriage. As we





landmark, in the far distance appears to remain unmoved during a

comparatively long time.


invariably accompanied by an apparent displacement of the objects about






Thus it comes to pass that distances can be measured without the







horizon will appear pretty much in the same direction. They would


sufficiently for the purpose of estimating their distance from it. It[Pg

58] is the same with regard to the moon. Two observers, standing upon


see the position of our satellite sufficiently altered with regard to


their calculations.










during the long journey of many millions of miles which our earth



measurements, is insufficient to show anything more than the tiniest



measuring instruments at their command were utterly inadequate to detect

such small displacements. It was reserved for the telescope to reveal


show the[Pg 59] slight changes in the position of the nearer stars,


orbit, and some six months later at the other end?stations separated


of miles.

The actual distances of certain celestial bodies being thus

ascertainable, it becomes a matter of no great difficulty to determine


experience that the size which any object appears to have, depends













points of light, that our mightiest telescopes cannot magnify them

sufficiently to show any breadth of surface.

Instead of saying that an object looks a certain[Pg 60] breadth across,





considered the moon and sun /look/ about the same size, or, as an






system, is technically known as its "disc."

[Pg 61]










said to /eclipse/ it. When it thus hides a planet or star, it is said to

/occult/ it. The reason why a separate term is used for what is merely a





small in comparison, that it is always /entirely swallowed up for some

time/ when it passes behind the body of our satellite.


blaze of sunlight.

By reason of the small size which the planets look[Pg 62] when viewed



the telescope, for the planetary bodies then display broad discs.


/transit/. This takes place when an apparently small body passes across







Transits of Mercury.

As the satellites of Jupiter are continually revolving around him, they

will often pass behind or across his disc. Such occultations and

transits of satellites can be well observed in the telescope.


obscured without the necessity of its being hidden from us by one






As the sun is very large, and the earth in comparison very[Pg 63] small,









what is called /full moon/, when she is on the other side of the earth



is not quite /upon the same plane/ with the earth's. It thus happens




darkening of her light is known as an /eclipse of the moon/. It seems a



body coming directly /between/ it and our eyes.



J.E. Gore[4] <#Footnote_4_4> puts it: "The darkening of the sun's light

by the interposition of the moon's body seems more[Pg 64] obvious than

the passing of the moon through the earth's shadow."

Eclipses of the moon furnish striking spectacles, but really add little



shadow when seen creeping over the moon's surface is always circular.

Fig. 3.

Fig. 3.?Total and Partial Eclipses of the Moon. The Moon is here shown

in two positions; i.e. /entirely/ plunged in the earth's shadow and

therefore totally eclipsed, and only /partly/ plunged in it or partially


/Eclipses of the Moon/, or Lunar Eclipses, as they are also called, are

of two kinds?/Total/, and /Partial/. In a total lunar eclipse the moon



shadow, and so only /part/ of her surface is darkened (see Fig. 3

<#Fig_3>). A very striking phenomenon during a total eclipse of the



that time should be /wholly/ cut off from it. The occasions indeed upon

which the moon has completely[Pg 65] disappeared from view during the



sometimes she has assumed an ashen hue. The explanations of these


which surrounds our earth. When those portions of our earth's atmosphere








disappears altogether for the time being from the night sky.

/Eclipses of the Sun/, otherwise known as Solar Eclipses, are divided

into /Total/, /Partial/, and /Annular/. A total eclipse of the sun takes


manner that it cuts off the sunlight /entirely/ for the time being from

a /portion/ of the earth's surface. A person situated in the region in
question will, therefore, at that moment find the sun temporarily





extent. In places not very distant[Pg 66] from this region, the moon




total will be always a comparatively narrow band lying roughly from west

to east. This band, known as the /track of totality/, can, at the





the sun (see Fig. 4 <#Fig_4> (i.), p. 67).


course of which the positions, where the eclipse would ordinarily be




only seen /partly eclipsed at the utmost/ (see Fig. 4 <#Fig_4> (ii.), p.

[Pg 67]

(i.) Total Eclipse of the Sun. (i.) Total Eclipse of the Sun.

(ii.) Partial Eclipse of the Sun. (ii.) Partial Eclipse of the Sun.

Fig. 4.?Total and Partial Eclipses of the Sun. From the position A the

Sun cannot be seen, as it is entirely blotted out by the Moon. From B it

is seen partially blotted out, because the Moon is to a certain degree

in the way. From C no eclipse is seen, because the Moon does not come in

the way.

It is to be noted that in a Partial Eclipse of the Sun, the position A

lies /outside/ the surface of the Earth.

An /Annular eclipse/ is an eclipse which just fails to become total for






occupies being known as the /focus/. The sun being at the focus of the










around the moon like a ring of light. This is what is known as[Pg 68] an

annular eclipse, from the Latin word /annulus/, which means a ring. The




the point.


must be always two such eclipses /at least/ during that period, though




solar and three lunar. This general statement refers merely to eclipses


will be total or partial.



modern astronomy would be but for the extraordinary coincidence which






this takes place the great blaze of sunlight which ordinarily dazzles



[Pg 69]





steadily across the solar face. Notwithstanding the gradual obscuration



begins to pervade all things, the temperature falls noticeably, and







rainstorm of great violence were approaching. This is caused by the


at the terrific velocity of about half a mile a second.

If the gradually diminishing crescent of sun be now watched through a

telescope, the observer will notice that it does not eventually vanish




upon, but the majority of astronomers incline to the opinion[Pg 70] that


between those lunar mountain peaks which happen at the moment to fringe





In a total Eclipse /In a total Eclipse/

In an annular Eclipse /In an annular Eclipse/

Fig. 5.?"Baily's Beads."

strange appearance, ordinarily unseen because of the blaze of sunlight.



other than the celebrated phenomenon widely known as the /Solar Corona/.


a lunar atmosphere illuminated by the sunlight shining through it from


when occulting them, has amply[Pg 71] proved that she possesses no

atmosphere worth speaking about. It is now, however, satisfactorily



across it.

All the time that the /total phase/ (as it is called) lasts, the corona

glows with its pale unearthly light, shedding upon the earth's surface

an illumination somewhat akin to full moonlight. Usually the planet


Meantime around the observer animal and plant life behave as at






side, the corona disappears.
There is another famous accompaniment of the sun which partly reveals



This layer is known by the name of the /Chromosphere/. Just as at







the[Pg 72] chromosphere in the form of a narrow red strip, fringing the



of a strip of chromosphere.






as the /Solar Prominences/. In the same way as the corona, the

chromosphere and prominences were for a time supposed to belong to the


disc was noticed to creep slowly across them also.



longer than about eight minutes.






entirely at an end.


of these accompaniments of the sun which a total eclipse reveals to

us.[Pg 73] Our further consideration of them must, however, be reserved








during the eclipse of 1869.

To the serious observer of a total solar eclipse every instant is

extremely precious. Many distinct observations have to be crowded into a







precaution has been taken, weather possibilities remain to be reckoned

with, so that success is rather a lottery.


the proper utilisation of which personal experience is of absolute

necessity. It was manifestly out of the question that such experience

could be gained by any individual in early times,[Pg 74] as the

imperfection of astronomical theory and geographical knowledge rendered










body of organised knowledge upon this subject was greatly delayed.

Nothing perhaps better shows the soundness of modern astronomical theory

than the almost exact agreement of the time predicted for an eclipse

with its actual occurrence. Similarly, by calculating backwards,

astronomers have discovered the times and seasons at which many ancient

eclipses took place, and valuable opportunities have thus arisen for

checking certain disputed dates in history.

It should not be omitted here that the ancients were actually able, /in

a rough way/, to predict eclipses. The Chaldean astronomers had indeed

noticed very early a curious circumstance, /i.e./ that eclipses tend to

repeat themselves after a lapse of slightly more than eighteen years.


instance, that the eclipses which[Pg 75] occur in any particular year





an equilibrium resulting from æons of orbital ebb and flow, naturally

tends to make the members which compose that family repeat their ancient

same order of things will /almost exactly/ recur. Thus, as a consequence


tend, after a period of 18 years and 10? days,[5] <#Footnote_5_5> to



comprised within it will be repeated in their order.

To give examples:?


August 19, 1887.


which took place on February 11, 1888.


28, 1889.


we come upon a total solar[Pg 76] eclipse predicted for September 10,


so on too with the others.


this remarkable generalisation; and they used it for the rough


of "Saros."



too little heed.

In order not to complicate matters unduly, the recurrence of solar




the moon.



at each recurrence are reproduced /almost exactly/. Here, then, lies the

/crux/ of the situation. For it is quite evident that were the

conditions /exactly/ reproduced, the recurrences of each eclipse would



situations which they had previously occupied, the recurrences of a

solar eclipse would tend to duplicate its forerunner with regard to the

position of the shadow upon the terrestrial surface. But the conditions
/not/ being exactly reproduced, the[Pg 77] shadow-track does not pass



shifted a little farther. Every solar eclipse has therefore a definite




an imaginary example. A /partial/ eclipse occurs, say, somewhere near












finally passes off. Our imaginary eclipse series is now no more?its

"life" has ended.

We have taken, as an example, an eclipse series moving from north to

south. We might have taken one moving from south to north, for they

progress in either direction.
From the description just given the reader might[Pg 78] suppose that, if

the tracks of totality of an eclipse series were plotted upon a chart of

the world, they would lie one beneath another like a set of steps. This

is, however, /not/ the case, and the reason is easily found. It depends

upon the fact that the saros does not comprise an exact number of days,

but includes, as we have seen, one-third of a day in addition.

It will be granted, of course, that if the number of days was exact, the

/same/ parts of the earth would always be brought round by the axial

rotation /to front the sun/ at the moment of the recurrence of the

eclipse. But as there is still one-third of a day to complete the saros

period, the earth has yet to make one-third of a rotation upon its axis

before the eclipse takes place. Thus at every recurrence the track of

totality finds itself placed one-third of the earth's circumference to

the /westward/. Three of the recurrences will, of course, complete the

circuit of the globe; and so the fourth recurrence will duplicate the

one which preceded it, three saros returns, or 54 years and 1 month

before. This duplication, as we have already seen, will, however, be

situated in a latitude to the south or north of its predecessor,

according as the eclipse series is progressing in a southerly or

northerly direction.

Lastly, every eclipse series, after working its way across the earth,

will return again to go through the same process after some 12,000
years; so that, at the end of that great lapse of time, the entire

"life" of every eclipse should repeat itself, provided that the

conditions of the solar system have not altered appreciably during the


[Pg 79]

We are now in a position to consider this gradual southerly or northerly

progress of eclipse recurrences in its application to the case of

eclipses of the moon. It should be evident that, just as in solar

eclipses the lunar shadow is lowered or raised (as the case may be) each

time it strikes the terrestrial surface, so in lunar eclipses will the

body of the moon shift its place at each recurrence relatively to the

position of the earth's shadow. Every lunar eclipse, therefore, will

commence on our satellite's disc as a partial eclipse at the northern or

southern extremity, as the case may be. Let us take, as an example, an

imaginary series of eclipses of the moon progressing from north to

south. At each recurrence the partial phase will grow greater, its

boundary encroaching more and more to the southward, until eventually

the whole disc is enveloped by the shadow, and the eclipse becomes

total. It will then repeat itself as total during a number of

recurrences, until the entire breadth of the shadow has been passed

through, and the northern edge of the moon at length springs out into

sunlight. This illuminated portion will grow more and more extensive at

each succeeding return, the edge of the shadow appearing to recede from
it until it finally passes off at the south. Similarly, when a lunar

eclipse commences as partial at the south of the moon, the edge of the

shadow at each subsequent recurrence finds itself more and more to the

northward. In due course the total phase will supervene, and will

persist during a number of recurrences until the southerly trend of the

moon results in the uncovering of the lunar surface at the south. Thus,

as the boundary of the shadow is left[Pg 80] more and more to the

northward, the illuminated portion on the southern side of the moon

becomes at each recurrence greater and the darkened portion on the

northern side less, until the shadow eventually passes off at the north.

The "life" of an eclipse of the moon happens, for certain reasons, to be

much shorter than that of an eclipse of the sun. It lasts during only

about 860 years, or 48 saros returns.

Fig. 6, p. 81, is a map of the world on Mercator's Projection, showing a

portion of the march of the total solar eclipse of August 30, 1905,

across the surface of the earth. The projection in question has been

employed because it is the one with which people are most familiar. This

eclipse began by striking the neighbourhood of the North Pole in the

guise of a partial eclipse during the latter part of the reign of Queen

Elizabeth, and became total on the earth for the first time on the 24th

of June 1797. Its next appearance was on the 6th of July 1815. It has

not been possible to show the tracks of totality of these two early

visitations on account of the distortion of the polar regions consequent
on the /fiction/ of Mercator's Projection. It is therefore made to

commence with the track of its third appearance, viz. on July 17, 1833.

In consequence of those variations in the apparent sizes of the sun and

moon, which result, as we have seen, from the variations in their

distances from the earth, this eclipse will change from a total into an

annular eclipse towards the end of the twenty-first century. By that

time the track will have passed to the southern side of the equator. The

track will eventually leave the earth near the South Pole about the

beginning of the twenty-sixth century, and the rear portion of the

partial shadow will in its turn be clear of the terrestrial surface by

about 2700 A.D., when the series comes to an end.

[Pg 81]

Fig. 6. Fig. 6.?Map of the World on Mercator's Projection, showing a

portion of the progress of the Total Solar Eclipse of August 30, 1905,

across the surface of the earth.

[Pg 82]

[4] <#FNanchor_4_4> Astronomical Essays (p. 40), London, 1907.

[5] <#FNanchor_5_5> In some cases the periods between the dates of the

corresponding eclipses /appear/ to include a greater number of days than

ten; but this is easily explained when allowance is made for intervening
/leap/ years (in each of which an /extra/ day has of course been added),

and also for variations in local time.


[Pg 83]



What is thought to be the earliest reference to an eclipse comes down to

us from the ancient Chinese records, and is over four thousand years

old. The eclipse in question was a solar one, and occurred, so far as

can be ascertained, during the twenty-second century B.C. The story runs

that the two state astronomers, Ho and Hi by name, being exceedingly

intoxicated, were unable to perform their required duties, which

consisted in superintending the customary rites of beating drums,

shooting arrows, and the like, in order to frighten away the mighty

dragon which it was believed was about to swallow up the Lord of Day.

This eclipse seems to have been only partial; nevertheless a great

turmoil ensued, and the two astronomers were put to death, no doubt with

the usual /celestial/ cruelty.
The next eclipse mentioned in the Chinese annals is also a solar

eclipse, and appears to have taken place more than a thousand years

later, namely in 776 B.C. Records of similar eclipses follow from the

same source; but as they are mere notes of the events, and do not enter

into any detail, they are of little interest. Curiously enough the

Chinese have taken practically no notice of eclipses of the moon, but

have left us a comparatively careful record of[Pg 84] comets, which has

been of value to modern astronomy.

The earliest mention of a /total/ eclipse of the sun (for it should be

noted that the ancient Chinese eclipse above-mentioned was merely

partial) was deciphered in 1905, on a very ancient Babylonian tablet, by

Mr. L.W. King of the British Museum. This eclipse took place in the year

1063 B.C.

Assyrian tablets record three solar eclipses which occurred between

three and four hundred years later than this. The first of these was in

763 B.C.; the total phase being visible near Nineveh.

The next record of an eclipse of the sun comes to us from a Grecian

source. This eclipse took place in 585 B.C., and has been the subject of

much investigation. Herodotus, to whom we are indebted for the account,

tells us that it occurred during a battle in a war which had been waging

for some years between the Lydians and Medes. The sudden coming on of
darkness led to a termination of the contest, and peace was afterwards

made between the combatants. The historian goes on to state that the

eclipse had been foretold by Thales, who is looked upon as the Founder

of Grecian astronomy. This eclipse is in consequence known as the

"Eclipse of Thales." It would seem as if that philosopher were

acquainted with the Chaldean saros.

The next solar eclipse worthy of note was an annular one, and occurred

in 431 B.C., the first year of the Peloponnesian War. Plutarch relates

that the pilot of the ship, which was about to convey Pericles to the

Peloponnesus, was very much frightened by it; but Pericles calmed him by

holding up a cloak[Pg 85] before his eyes, and saying that the only

difference between this and the eclipse was that something larger than

the cloak prevented his seeing the sun for the time being.

An eclipse of great historical interest is that known as the "Eclipse of

Agathocles," which occurred on the morning of the 15th of August, 310

B.C. Agathocles, Tyrant of Syracuse, had been blockaded in the harbour

of that town by the Carthaginian fleet, but effected the escape of his

squadron under cover of night, and sailed for Africa in order to invade

the enemy's territory. During the following day he and his vessels

experienced a total eclipse, in which "day wholly put on the appearance

of night, and the stars were seen in all parts of the sky."

A few solar eclipses are supposed to be referred to in early Roman
history, but their identity is very doubtful in comparison with those

which the Greeks have recorded. Additional doubt is cast upon them by

the fact that they are usually associated with famous events. The birth

and death of Romulus, and the Passage of the Rubicon by Julius Cæsar,

are stated indeed to have been accompanied by these marks of the

approval or disapproval of the gods!

Reference to our subject in the Bible is scanty. Amos viii. 9 is thought

to refer to the Nineveh eclipse of 763 B.C., to which allusion has

already been made; while the famous episode of Hezekiah and the shadow

on the dial of Ahaz has been connected with an eclipse which was partial

at Jerusalem in 689 B.C.

The first solar eclipse, recorded during the Christian Era, is known as

the "Eclipse of Phlegon," from the fact that we are indebted for the

account to a pagan writer[Pg 86] of that name. This eclipse took place

in A.D. 29, and the total phase was visible a little to the north of

Palestine. It has sometimes been confounded with the "darkness of the

Crucifixion," which event took place near the date in question; but it

is sufficient here to say that the Crucifixion is well known to have

occurred during the Passover of the Jews, which is always celebrated at

the /full/ moon, whereas an eclipse of the sun can only take place at

/new/ moon.

Dion Cassius, commenting on the Emperor Claudius about the year A.D. 45,
writes as follows:?

"As there was going to be an eclipse on his birthday, through fear of a

disturbance, as there had been other prodigies, he put forth a public

notice, not only that the obscuration would take place, and about the

time and magnitude of it, but also about the causes that produce such an


This is a remarkable piece of information; for the Romans, an

essentially military nation, appear hitherto to have troubled themselves

very little about astronomical matters, and were content, as we have

seen, to look upon phenomena, like eclipses, as mere celestial prodigies.

What is thought to be the first definite mention of the solar corona

occurs in a passage of Plutarch. The eclipse to which he refers is

probably one which took place in A.D. 71. He says that the obscuration

caused by the moon "has no time to last and no extensiveness, but some

light shows itself round the sun's circumference, which does not allow

the darkness to become deep and complete." No further reference to this

phenomenon occurs until near the end of the sixteenth century. It

should, however, be here[Pg 87] mentioned that Mr. E.W. Maunder has

pointed out the probability[6] <#Footnote_6_6> that we have a very

ancient symbolic representation of the corona in the "winged circle,"

"winged disc," or "ring with wings," as it is variously called, which

appears so often upon Assyrian and Egyptian monuments, as the symbol of
the Deity (Fig. 7).

Fig. 7.

Fig. 7.?The "Ring with Wings." The upper is the Assyrian form of the

symbol, the lower the Egyptian. (From /Knowledge/.) Compare the form of

the corona on Plate VII. <#Plate_VII> (B), p. 142.

The first solar eclipse recorded to have been seen in England is that of

A.D. 538, mention of which is found in the /Anglo-Saxon Chronicle/. The

track of totality did not, however, come near our islands, for only

two-thirds of the sun's disc were eclipsed at London.

[Pg 88]

In 840 a great eclipse took place in Europe, which was total for more

than five minutes across what is now Bavaria. Terror at this eclipse is

said to have hastened the death of Louis le Debonnaire, Emperor of the

West, who lay ill at Worms.

In 878?/temp./ King Alfred?an eclipse of the sun took place which was

total at London. From this until 1715 no other eclipse was total at

London itself; though this does not apply to other portions of England.

An eclipse, generally known as the "Eclipse of Stiklastad," is said to

have taken place in 1030, during the sea-fight in which Olaf of Norway
is supposed to have been slain. Longfellow, in his /Saga of King Olaf/,

has it that

"The Sun hung red

As a drop of blood,"

but, as in the case of most poets, the dramatic value of an eclipse

seems to have escaped his notice.

In the year 1140 there occurred a total eclipse of the sun, the last to

be visible in England for more than five centuries. Indeed there have

been only two such since?namely, those of 1715 and 1724, to which we

shall allude in due course. The eclipse of 1140 took place on the 20th

March, and is thus referred to in the /Anglo-Saxon Chronicle/:?

"In the Lent, the sun and the day darkened, about the noon-tide of the

day, when men were eating, and they lighted candles to eat by. That was

the 13th day before the calends of April. Men were very much struck with


Several of the older historians speak of a "fearful eclipse" as having

taken place on the morning of the[Pg 89] Battle of Crecy, 1346. Lingard,

for instance, in his /History of England/, has as follows:?

"Never, perhaps, were preparations for battle made under circumstances
so truly awful. On that very day the sun suffered a partial eclipse:

birds, in clouds, the precursors of a storm, flew screaming over the two


and lightning. About five in the afternoon the weather cleared up; the

sun in full splendour darted his rays in the eyes of the enemy."

Calculations, however, show that no eclipse of the sun took place in

Europe during that year. This error is found to have arisen from the

mistranslation of an obsolete French word /esclistre/ (lightning), which

is employed by Froissart in his description of the battle.

In 1598 an eclipse was total over Scotland and part of North Germany. It

was observed at Torgau by Jessenius, an Hungarian physician, who noticed

a bright light around the moon during the time of totality. This is said

to be the first reference to the corona since that of Plutarch, to which

we have already drawn attention.

Mention of Scotland recalls the fact that an unusual number of eclipses

happen to have been visible in that country, and the occult bent natural

to the Scottish character has traditionalised a few of them in such

terms as the "Black Hour" (an eclipse of 1433), "Black Saturday" (the

eclipse of 1598 which has been alluded to above), and "Mirk Monday"

(1652). The track of the last-named also passed over Carrickfergus in

Ireland, where it was observed by a certain Dr. Wybord, in whose account

the[Pg 90] term "corona" is first employed. This eclipse is the last
which has been total in Scotland, and it is calculated that there will

not be another eclipse seen as total there until the twenty-second century.

An eclipse of the sun which took place on May 30, 1612, is recorded as

having been seen "through a tube." This probably refers to the then

recent invention?the telescope.

The eclipses which we have been describing are chiefly interesting from

an historical point of view. The old mystery and confusion to the

beholders seem to have lingered even into comparatively enlightened

times, for we see how late it is before the corona attracts definite

attention for the sake of itself alone.

It is not a far cry from notice of the corona to that of other

accompaniments of a solar eclipse. Thus the eclipse of 1706, the total

phase of which was visible in Switzerland, is of great interest; for it

was on this occasion that the famous red prominences seem first to have

been noted. A certain Captain Stannyan observed this eclipse from Berne

in Switzerland, and described it in a letter to Flamsteed, the then

Astronomer Royal. He says the sun's "getting out of his eclipse was

preceded by a blood-red streak of light from its left limb, which

continued not longer than six or seven seconds of time; then part of the

Sun's disc appeared all of a sudden, as bright as Venus was ever seen in

the night, nay brighter; and in that very instant gave a Light and

Shadow to things as strong as Moonlight uses to do." How little was then
expected of the sun is, however, shown by Flamsteed's words, when

communicating this information to the Royal Society:?

[Pg 91]

"The Captain is the first man I ever heard of that took notice of a Red

Streak of Light preceding the Emersion of the Sun's body from a total

Eclipse. And I take notice of it to you because it infers that /the Moon

has an atmosphere/; and its short continuance of only six or seven

seconds of time, tells us that /its height is not more than the five or

six hundredth part of her diameter/."

What a change has since come over the ideas of men! The sun has proved a

veritable mine of discovery, while the moon has yielded up nothing new.

The eclipse of 1715, the first total at London since that of 878, was

observed by the famous astronomer, Edmund Halley, from the rooms of the

Royal Society, then in Crane Court, Fleet Street. On this occasion both

the corona and a red projection were noted. Halley further makes

allusion to that curious phenomenon, which later on became celebrated

under the name of "Baily's beads." It was also on the occasion of this

eclipse that the /earliest recorded drawings of the corona/ were made.

Cambridge happened to be within the track of totality; and a certain

Professor Cotes of that University, who is responsible for one of the

drawings in question, forwarded them to Sir Isaac Newton together with a
letter describing his observations.

In 1724 there occurred an eclipse, the total phase of which was visible

from the south-west of England, but not from London. The weather was

unfavourable, and the eclipse consequently appears to have been seen by

only one person, a certain Dr. Stukeley, who observed it from Haraden

Hill near Salisbury Plain. This is the last eclipse of which the

total[Pg 92] phase was seen in any part of England. The next will not be

until June 29, 1927, and will be visible along a line across North Wales

and Lancashire. The discs of the sun and moon will just then be almost

of the same apparent size, and so totality will be of extremely short

duration; in fact only a few seconds. London itself will not see a

totality until the year 2151?a circumstance which need hardly distress

any of us personally!

It is only from the early part of the nineteenth century that serious

scientific attention to eclipses of the sun can be dated. An /annular/

eclipse, visible in 1836 in the south of Scotland, drew the careful

notice of Francis Baily of Jedburgh in Roxburghshire to that curious

phenomenon which we have already described, and which has ever since

been known by the name of "Baily's beads." Spurred by his observation,

the leading astronomers of the day determined to pay particular

attention to a total eclipse, which in the year 1842 was to be visible

in the south of France and the north of Italy. The public interest

aroused on this occasion was also very great, for the region across
which the track of totality was to pass was very populous, and inhabited

by races of a high degree of culture.

This eclipse occurred on the morning of the 8th July, and from it may be

dated that great enthusiasm with which total eclipses of the sun have

ever since been received. Airy, our then Astronomer Royal, observed it

from Turin; Arago, the celebrated director of the Paris Observatory,

from Perpignan in the south of France; Francis Baily from Pavia; and Sir

John Herschel from Milan. The corona[Pg 93] and three large red

prominences were not only well observed by the astronomers, but drew

tremendous applause from the watching multitudes.

The success of the observations made during this eclipse prompted

astronomers to pay similar attention to that of July 28, 1851, the total

phase of which was to be visible in the south of Norway and Sweden, and

across the east of Prussia. This eclipse was also a success, and it was

now ascertained that the red prominences belonged to the sun and not to

the moon; for the lunar disc, as it moved onward, was seen to cover and

to uncover them in turn. It was also noted that these prominences were

merely uprushes from a layer of glowing gaseous matter, which was seen

closely to envelop the sun.

The total eclipse of July 18, 1860, was observed in Spain, and

photography was for the first time /systematically/ employed in its

observation.[7] <#Footnote_7_7> In the photographs taken the stationary
appearance of both the corona and prominences with respect to the moving

moon, definitely confirmed the view already put forward that they were

actual appendages of the sun.

The eclipse of August 18, 1868, the total phase of which lasted nearly

six minutes, was visible in India, and drew thither a large concourse of

astronomers. In this eclipse the spectroscope came to the front, and

showed that both the prominences, and the chromospheric layer from which

they rise, are composed of glowing vapours?chief among which is the[Pg

94] vapour of hydrogen. The direct result of the observations made on

this occasion was the spectroscopic method of examining prominences at

any time in full daylight, and without a total eclipse. This method,

which has given such an immense impetus to the study of the sun, was the

outcome of independent and simultaneous investigation on the part of the

French astronomer, the late M. Janssen, and the English astronomer,

Professor (now Sir Norman) Lockyer, a circumstance strangely reminiscent

of the discovery of Neptune. The principles on which the method was

founded seem, however, to have occurred to Dr. (now Sir William) Huggins

some time previously.

The eclipse of December 22, 1870, was total for a little more than two

minutes, and its track passed across the Mediterranean. M. Janssen, of

whom mention has just been made, escaped in a balloon from then besieged

Paris, taking his instruments with him, and made his way to Oran, in

Algeria, in order to observe it; but his expectations were disappointed
by cloudy weather. The expedition sent out from England had the

misfortune to be shipwrecked off the coast of Sicily. But the occasion

was redeemed by a memorable observation made by the American astronomer,

the late Professor Young, which revealed the existence of what is now

known as the "Reversing Layer." This is a shallow layer of gases which

lies immediately beneath the chromosphere. An illustration of the

corona, as it was seen during the above eclipse, will be found on Plate

VII. <#Plate_VII> (A), p. 142.

In the eclipse of December 12, 1871, total across Southern India, the

photographs of the corona obtained by Mr. Davis, assistant to Lord

Lindsay (now[Pg 95] the Earl of Crawford), displayed a wealth of detail

hitherto unapproached.

The eclipse of July 29, 1878, total across the western states of North

America, was a remarkable success, and a magnificent view of the corona

was obtained by the well-known American astronomer and physicist, the

late Professor Langley, from the summit of Pike's Peak, Colorado, over

14,000 feet above the level of the sea. The coronal streamers were seen

to extend to a much greater distance at this altitude than at points

less elevated, and the corona itself remained visible during more than

four minutes after the end of totality. It was, however, not entirely a

question of altitude; the coronal streamers were actually very much

longer on this occasion than in most of the eclipses which had

previously been observed.
The eclipse of May 17, 1882, observed in Upper Egypt, is notable from

the fact that, in one of the photographs taken by Dr. Schuster at Sohag,

a bright comet appeared near the outer limit of the corona (see Plate I.

<#Plate_I>, p. 96). The comet in question had not been seen before the

eclipse, and was never seen afterwards. This is the third occasion on

which attention has been drawn to a comet /merely/ by a total eclipse.

The first is mentioned by Seneca; and the second by Philostorgius, in an

account of an eclipse observed at Constantinople in A.D. 418. A fourth

case of the kind occurred in 1893, when faint evidences of one of these

filmy objects were found on photographs of the corona taken by the

American astronomer, Professor Schaeberle, during the total eclipse of

April 16 of that year.

The eclipse of May 6, 1883, had a totality of over[Pg 96] five minutes,

but the central track unfortunately passed across the Pacific Ocean, and

the sole point of land available for observing it from was one of the

Marquesas Group, Caroline Island, a coral atoll seven and a half miles

long by one and a half broad. Nevertheless astronomers did not hesitate

to take up their posts upon that little spot, and were rewarded with

good weather.

The next eclipse of importance was that of April 16, 1893. It stretched

from Chili across South America and the Atlantic Ocean to the West Coast

of Africa, and, as the weather was fine, many good results were
obtained. Photographs were taken at both ends of the track, and these

showed that the appearance of the corona remained unchanged during the

interval of time occupied by the passage of the shadow across the earth.

It was on the occasion of this eclipse that Professor Schaeberle found

upon his photographs those traces of the presence of a comet, to which

allusion has already been made.

Extensive preparations were made to observe the eclipse of August 9,

1896. Totality lasted from two to three minutes, and the track stretched

from Norway to Japan. Bad weather disappointed the observers, with the

exception of those taken to Nova Zembla by Sir George Baden Powell in

his yacht /Otaria/.

The eclipse of January 22, 1898, across India /viâ/ Bombay and Benares,

was favoured with good weather, and is notable for a photograph obtained

by Mrs. E.W. Maunder, which showed a ray of the corona extending to a

most unusual distance.

Plate I.

Plate I. The Total Eclipse of the Sun of May 17th, 1882

A comet is here shown in the immediate neighbourhood of the corona.

Drawn by Mr. W.H. Wesley from the photographs.

(Page 95 <#Page_95>)

[Pg 97]
Of very great influence in the growth of our knowledge with regard to

the sun, is the remarkable piece of good fortune by which the countries

around the Mediterranean, so easy of access, have been favoured with a

comparatively large number of total eclipses during the past sixty

years. Tracks of totality have, for instance, traversed the Spanish

peninsula on no less than five occasions during that period. Two of

these are among the most notable eclipses of recent years, namely, those

of May 28, 1900, and of August 30, 1905. In the former the track of

totality stretched from the western seaboard of Mexico, through the

Southern States of America, and across the Atlantic Ocean, after which

it passed over Portugal and Spain into North Africa. The total phase

lasted for about a minute and a half, and the eclipse was well observed

from a great many points along the line. A representation of the corona,

as it appeared on this occasion, will be found on Plate VII.

<#Plate_VII> (B), p. 142.

The track of the other eclipse to which we have alluded, /i.e./ that of

August 30, 1905, crossed Spain about 200 miles to the northward of that

of 1900. It stretched from Winnipeg in Canada, through Labrador, and

over the Atlantic; then traversing Spain, it passed across the Balearic

Islands, North Africa, and Egypt, and ended in Arabia (see Fig. 6

<#Fig_6>, p. 81). Much was to be expected from a comparison between the

photographs taken in Labrador and Egypt on the question as to whether

the corona would show any alteration in shape during the time that the
shadow was traversing the intervening space?some 6000 miles. The

duration of the total phase in this eclipse was nearly four minutes. Bad

weather, however, interfered a good deal with the observations. It was

not possible, for instance, to do anything at all[Pg 98] in Labrador. In

Spain the weather conditions were by no means favourable; though at

Burgos, where an immense number of people had assembled, the total phase

was, fortunately, well seen. On the whole, the best results were

obtained at Guelma in Algeria. The corona on the occasion of this

eclipse was a very fine one, and some magnificent groups of prominences

were plainly visible to the naked eye (see the Frontispiece


The next total eclipse after that of 1905 was one which occurred on

January 14, 1907. It passed across Central Asia and Siberia, and had a

totality lasting two and a half minutes at most; but it was not observed

as the weather was extremely bad, a circumstance not surprising with

regard to those regions at that time of year.

The eclipse of January 3, 1908, passed across the Pacific Ocean. Only

two small coral islands?Hull Island in the Ph?nix Group, and Flint

Island about 400 miles north of Tahiti?lay in the track. Two expeditions

set out to observe it, /i.e./ a combined American party from the Lick

Observatory and the Smithsonian Institution of Washington, and a private

one from England under Mr. F.K. McClean. As Hull Island afforded few

facilities, both parties installed their instruments on Flint Island,
although it was very little better. The duration of the total phase was

fairly long?about four minutes, and the sun very favourably placed,

being nearly overhead. Heavy rain and clouds, however, marred

observation during the first minute of totality, but the remaining three

minutes were successfully utilised, good photographs of the corona being


[Pg 99]

The next few years to come are unfortunately by no means favourable from

the point of view of the eclipse observer. An eclipse will take place on

June 17, 1909, the track stretching from Greenland across the North

Polar regions into Siberia. The geographical situation is, however, a

very awkward one, and totality will be extremely short?only six seconds

in Greenland and twenty-three seconds in Siberia.

The eclipse of May 9, 1910, will be visible in Tasmania. Totality will

last so long as four minutes, but the sun will be at the time much too

low in the sky for good observation.

The eclipse of the following year, April 28, 1911, will also be

confined, roughly speaking, to the same quarter of the earth, the track

passing across the old convict settlement of Norfolk Island, and then

out into the Pacific.
The eclipse of April 17, 1912, will stretch from Portugal, through

France and Belgium into North Germany. It will, however, be of

practically no service to astronomy. Totality, for instance, will last

for only three seconds in Portugal; and, though Paris lies in the

central track, the eclipse, which begins as barely total, will have

changed into an /annular/ one by the time it passes over that city.

The first really favourable eclipse in the near future will be that of

August 21, 1914. Its track will stretch from Greenland across Norway,

Sweden, and Russia. This eclipse is a return, after one saros, of the

eclipse of August 9, 1896.

The last solar eclipse which we will touch upon is that predicted for

June 29, 1927. It has been already alluded to as the first of those in

the future[Pg 100] to be /total/ in England. The central line will

stretch from Wales in a north-easterly direction. Stonyhurst

Observatory, in Lancashire, will lie in the track; but totality there

will be very short, only about twenty seconds in duration.

[6] <#FNanchor_6_6> /Knowledge/, vol. xx. p. 9, January 1897.

[7] <#FNanchor_7_7> The /first photographic representation of the

corona/ had, however, been made during the eclipse of 1851. This was a

daguerreotype taken by Dr. Busch at Königsberg in Prussia.

[Pg 101]



The earliest lunar eclipse, of which we have any trustworthy

information, was a total one which took place on the 19th March, 721

B.C., and was observed from Babylon. For our knowledge of this eclipse

we are indebted to Ptolemy, the astronomer, who copied it, along with

two others, from the records of the reign of the Chaldean king,


The next eclipse of the moon worth noting was a total one, which took

place some three hundred years later, namely, in 425 B.C. This eclipse

was observed at Athens, and is mentioned by Aristophanes in his play,

/The Clouds/.

Plutarch relates that a total eclipse of the moon, which occurred in 413

B.C., so greatly frightened Nicias, the general of the Athenians, then

warring in Sicily, as to cause a delay in his retreat from Syracuse
which led to the destruction of his whole army.

Seven years later?namely, in 406 B.C., the twenty-sixth year of the

Peloponnesian War?there took place another total lunar eclipse of which

mention is made by Xenophon.

Omitting a number of other eclipses alluded to by ancient writers, we

come to one recorded by Josephus as having occurred a little before the

death of Herod the Great. It is probable that the eclipse in question[Pg

102] was the total lunar one, which calculation shows to have taken

place on the 15th September 5 B.C., and to have been visible in Western

Asia. This is very important, for we are thus enabled to fix that year

as the date of the birth of Christ, for Herod is known to have died in

the early part of the year following the Nativity.

In those accounts of total lunar eclipses, which have come down to us

from the Dark and Middle Ages, the colour of the moon is nearly always

likened to "blood." On the other hand, in an account of the eclipse of

January 23, A.D. 753, our satellite is described as "covered with a

horrid black shield." We thus have examples of the two distinct

appearances alluded to in Chapter VII. <#CHAPTER_VII>, /i.e./ when the

moon appears of a coppery-red colour, and when it is entirely darkened.

It appears, indeed, that, in the majority of lunar eclipses on record,

the moon has appeared of a ruddy, or rather of a coppery hue, and the
details on its surface have been thus rendered visible. One of the best

examples of a /bright/ eclipse of this kind is that of the 19th March

1848, when the illumination of our satellite was so great that many

persons could not believe that an eclipse was actually taking place. A

certain Mr. Foster, who observed this eclipse from Bruges, states that

the markings on the lunar disc were almost as visible as on an "ordinary

dull moonlight night." He goes on to say that the British Consul at

Ghent, not knowing that there had been any eclipse, wrote to him for an

explanation of the red colour of the moon on that evening.

Out of the /dark/ eclipses recorded, perhaps the[Pg 103] best example is

that of May 18, 1761, observed by Wargentin at Stockholm. On this

occasion the lunar disc is said to have disappeared so completely, that

it could not be discovered even with the telescope. Another such

instance is the eclipse of June 10, 1816, observed from London. The

summer of that year was particularly wet?a point worthy of notice in

connection with the theory that these different appearances are due to

the varying state of our earth's atmosphere.

Sometimes, indeed, it has happened that an eclipse of the moon has

partaken of both appearances, part of the disc being visible and part

invisible. An instance of this occurred in the eclipse of July 12, 1870,

when the late Rev. S.J. Johnson, one of the leading authorities on

eclipses, who observed it, states that he found one-half the moon's

surface quite invisible, both with the naked eye and with the telescope.
In addition to the examples given above, there are three total lunar

eclipses which deserve especial mention.

1. A.D. 755, November 23. During the progress of this eclipse the moon

occulted the star Aldebaran in the constellation of Taurus.

2. A.D. 1493, April 2. This is the celebrated eclipse which is said to

have so well served the purposes of Christopher Columbus. Certain

natives having refused to supply him with provisions when in sore

straits, he announced to them that the moon would be darkened as a sign

of the anger of heaven. When the event duly came to pass, the savages

were so terrified that they brought him provisions as much as he needed.

[Pg 104]

3. A.D. 1610, July 6. The eclipse in question is notable as having been

seen through the telescope, then a recent invention. It was without

doubt the first so observed, but unfortunately the name of the observer

has not come down to us.


[Pg 105]


The earliest astronomical observations must have been made in the Dawn

of Historic Time by the men who tended their flocks upon the great

plains. As they watched the clear night sky they no doubt soon noticed

that, with the exception of the moon and those brilliant wandering

objects known to us as the planets, the individual stars in the heaven

remained apparently fixed with reference to each other. These seemingly

changeless points of light came in time to be regarded as sign-posts to

guide the wanderer across the trackless desert, or the voyager upon the

wide sea.

Just as when looking into the red coals of a fire, or when watching the

clouds, our imagination conjures up strange and grotesque forms, so did

the men of old see in the grouping of the stars the outlines of weird

and curious shapes. Fed with mythological lore, they imagined these to

be rough representations of ancient heroes and fabled beasts, whom they

supposed to have been elevated to the heavens as a reward for great

deeds done upon the earth. We know these groupings of stars to-day under

the name of the Constellations. Looking up at them we find it extremely

difficult to fit in the majority with the figures which the ancients
believed them to represent.[Pg 106] Nevertheless, astronomy has accepted

the arrangement, for want of a better method of fixing the leading stars

in the memory.

Our early ancestors lived the greater part of their lives in the open

air, and so came to pay more attention in general to the heavenly orbs

than we do. Their clock and their calendar was, so to speak, in the

celestial vault. They regulated their hours, their days, and their

nights by the changing positions of the sun, the moon, and the stars;

and recognised the periods of seed-time and harvest, of calm and stormy

weather, by the rising or setting of certain well-known constellations.

Students of the classics will recall many allusions to this, especially

in the Odes of Horace.

As time went on and civilisation progressed, men soon devised measuring

instruments, by means of which they could note the positions of the

celestial bodies in the sky with respect to each other; and, from

observations thus made, they constructed charts of the stars. The

earliest complete survey of this kind, of which we have a record, is the

great Catalogue of stars which was made, in the second century B.C., by

the celebrated Greek astronomer, Hipparchus, and in which he is said to

have noted down about 1080 stars.

It is unnecessary to follow in detail the tedious progress of

astronomical discovery prior to the advent of the telescope. Certain it
is that, as time went on, the measuring instruments to which we have

alluded had become greatly improved; but, had they even been perfect,

they would have been utterly inadequate to reveal those minute

displacements, from which we have learned the actual distance of the

nearest of the[Pg 107] celestial orbs. From the early times, therefore,

until the mediæval period of our own era, astronomy grew up upon a

faulty basis, for the earth ever seemed so much the largest body in the

universe, that it continued from century to century to be regarded as

the very centre of things.

To the Arabians is due the credit of having kept alive the study of the

stars during the dark ages of European history. They erected some fine

observatories, notably in Spain and in the neighbourhood of Bagdad.

Following them, some of the Oriental peoples embraced the science in

earnest; Ulugh Beigh, grandson of the famous Tamerlane, founding, for

instance, a great observatory at Samarcand in Central Asia. The Mongol

emperors of India also established large astronomical instruments in the

chief cities of their empire. When the revival of learning took place in

the West, the Europeans came to the front once more in science, and

rapidly forged ahead of those who had so assiduously kept alight the

lamp of knowledge through the long centuries.

The dethronement of the older theories by the Copernican system, in

which the earth was relegated to its true place, was fortunately soon

followed by an invention of immense import, the invention of the
Telescope. It is to this instrument, indeed, that we are indebted for

our knowledge of the actual scale of the celestial distances. It

penetrated the depths of space; it brought the distant orbs so near,

that men could note the detail on the planets, or measure the small

changes in their positions in the sky which resulted from the movement

of our own globe.

It was in the year 1609 that the telescope was first[Pg 108]

constructed. A year or so previous to this a spectacle-maker of

Middleburgh in Holland, one Hans Lippershey, had, it appears, hit upon

the fact that distant objects, when viewed through certain glass lenses

suitably arranged, looked nearer.[8] <#Footnote_8_8> News of this

discovery reached the ears of Galileo Galilei, of Florence, the foremost

philosopher of the day, and he at once applied his great scientific

attainments to the construction of an instrument based upon this

principle. The result was what was called an "optick tube," which

magnified distant objects some few times. It was not much larger than

what we nowadays contemptuously refer to as a "spy-glass," yet its

employment upon the leading celestial objects instantly sent

astronomical science onward with a bound. In rapid succession Galileo

announced world-moving discoveries; large spots upon the face of the

sun; crater-like mountains upon the moon; four subordinate bodies, or

satellites, circling around the planet Jupiter; and a strange appearance

in connection with Saturn, which later telescopic observers found to be

a broad flat ring encircling that planet. And more important still, the
magnified image of Venus showed itself in the telescope at certain

periods in crescent and other forms; a result which Copernicus is said

to have announced should of necessity follow if his system were the true


[Pg 109]

The discoveries made with the telescope produced, as time went on, a

great alteration in the notions of men with regard to the universe at

large. It must have been, indeed, a revelation to find that those points

of light which they called the planets, were, after all, globes of a

size comparable with the earth, and peopled perchance with sentient

beings. Even to us, who have been accustomed since our early youth to

such an idea, it still requires a certain stretch of imagination to

enlarge, say, the Bright Star of Eve, into a body similar in size to our

earth. The reader will perhaps recollect Tennyson's allusion to this in

/Locksley Hall, Sixty Years After/:?

"Hesper?Venus?were we native to that splendour or in Mars,


"Could we dream of wars and carnage, craft and madness, lust and spite,

Roaring London, raving Paris, in that point of peaceful light?"

The form of instrument as devised by Galileo is called the Refracting
Telescope, or "Refractor." As we know it to-day it is the same in

principle as his "optick tube," but it is not quite the same in

construction. The early /object-glass/, or large glass at the end, was a

single convex lens (see Fig. 8 <#Fig_8>, p. 113, "Galilean"); the modern

one is, on the other hand, composed of two lenses fitted together. The

attempts to construct large telescopes of the Galilean type met in

course of time with a great difficulty. The magnified image of the

object observed was not quite pure; its edges, indeed, were fringed with

rainbow-like colours. This defect was found to be aggravated with

increase in the size of object-glasses. A method was, however,[Pg 110]

discovered of diminishing this colouration, or /chromatic aberration/ as

it is called from the Greek word ????? (/chroma/), which means colour,

viz. by making telescopes of great length and only a few inches in

width. But the remedy was, in a way, worse than the disease; for

telescopes thus became of such huge proportions as to be too unwieldy

for use. Attempts were made to evade this unwieldiness by constructing

them with skeleton tubes (see Plate II. <#Plate_II>, p. 110), or,

indeed, even without tubes at all; the object-glass in the tubeless or

"aerial" telescope being fixed at the top of a high post, and the

/eye-piece/, that small lens or combination of lenses, which the eye

looks directly into, being kept in line with it by means of a string and

man?uvred about near the ground (Plate III. <#Plate_III>, p. 112). The

idea of a telescope without a tube may appear a contradiction in terms;

but it is not really so, for the tube adds nothing to the magnifying

power of the instrument, and is, in fact, no more than a mere device for
keeping the object-glass and eye-piece in a straight line, and for

preventing the observer from being hindered by stray lights in his

neighbourhood. It goes without saying, of course, that the image of a

celestial object will be more clear and defined when examined in the

darkness of a tube.

The ancients, though they knew nothing of telescopes, had, however,

found out the merit of a tube in this respect; for they employed simple

tubes, blackened on the inside, in order to obtain a clearer view of

distant objects. It is said that Julius Cæsar, before crossing the

Channel, surveyed the opposite coast of Britain through a tube of this kind.

Plate II. Plate II. Great Telescope of Hevelius

This instrument, 150 feet in length, with a /skeleton/ tube, was

constructed by the celebrated seventeenth century astronomer, Hevelius

of Danzig. From an illustration in the /Machina Celestis/.

(Page 110 <#Page_110>)

[Pg 111]

A few of the most famous of the immensely long telescopes above alluded

to are worthy of mention. One of these, 123 feet in length, was

presented to the Royal Society of London by the Dutch astronomer

Huyghens. Hevelius of Danzig constructed a skeleton one of 150 feet in

length (see Plate II. <#Plate_II>, p. 110). Bradley used a tubeless one
212 feet long to measure the diameter of Venus in 1722; while one of 600

feet is said to have been constructed, but to have proved quite unworkable!

Such difficulties, however, produced their natural result. They set men

at work to devise another kind of telescope. In the new form, called the

Reflecting Telescope, or "Reflector," the light coming from the object

under observation was /reflected/ into the eye-piece from the surface of

a highly polished concave metallic mirror, or /speculum/, as it was

called. It is to Sir Isaac Newton that the world is indebted for the

reflecting telescope in its best form. That philosopher had set himself

to investigate the causes of the rainbow-like, or prismatic colours

which for a long time had been such a source of annoyance to telescopic

observers; and he pointed out that, as the colours were produced in the

passage of the rays of light /through/ the glass, they would be entirely

absent if the light were reflected from the /surface/ of a mirror instead.

The reflecting telescope, however, had in turn certain drawbacks of its

own. A mirror, for instance, can plainly never be polished to such a

high degree as to reflect as much light as a piece of transparent glass

will let through. Further, the position of the eye-piece is by no means

so convenient. It cannot, of course, be pointed directly towards the

mirror, for the observer would then have to place his head right[Pg 112]

in the way of the light coming from the celestial object, and would

thus, of course, cut it off. In order to obviate this difficulty, the

following device was employed by Newton in his telescope, of which he
constructed his first example in 1668. A small, flat mirror was fixed by

thin wires in the centre of the tube of the telescope, and near to its

open end. It was set slant-wise, so that it reflected the rays of light

directly into the eye-piece, which was screwed into a hole at the side

of the tube (see Fig. 8 <#Fig_8>, p. 113, "Newtonian").

Although the Newtonian form of telescope had the immense advantage of

doing away with the prismatic colours, yet it wasted a great deal of

light; for the objection in this respect with regard to loss of light by

reflection from the large mirror applied, of course, to the small mirror

also. In addition, the position of the "flat," as the small mirror is

called, had the further effect of excluding from the great mirror a

certain proportion of light. But the reflector had the advantage, on the

other hand, of costing less to make than the refractor, as it was not

necessary to procure flawless glass for the purpose. A disc of a certain

metallic composition, an alloy of copper and tin, known in consequence

as /speculum metal/, had merely to be cast; and this had to be ground

and polished /upon one side only/, whereas a lens has to be thus treated

/upon both its sides/. It was, therefore, possible to make a much larger

instrument at a great deal less labour and expense.

Plate III. Plate III. A Tubeless, or "Aerial" Telescope

From an illustration in the /Opera Varia/ of Christian Huyghens.

(Page 110 <#Page_110>)
[Pg 113]

Fig. 8.

Fig. 8.?The various types of Telescope. All the above telescopes are

/pointed/ in the same direction; that is to say, the rays of light from

the object are coming from the left-hand side.

We have given the Newtonian form as an example of the principle of the

reflecting telescope. A somewhat similar instrument had, however, been

projected, though not actually constructed, by James Gregory a few years

earlier than Newton's, /i.e./ in 1663. In this form of reflector, known

as the "Gregorian" telescope, a hole was made in the big concave mirror;

and a small mirror, also concave, which faced it at a[Pg 114] certain

distance, received the reflected rays, and reflected them back again

through the hole in question into the eye-piece, which was fixed just

behind (see Fig. 8 <#Fig_8>, p. 113, "Gregorian"). The Gregorian had

thus the sentimental advantage of being /pointed directly at the

object/. The hole in the big mirror did not cause any loss of light, for

the central portion in which it was made was anyway unable to receive

light through the small mirror being directly in front of it. An

adaptation of the Gregorian was the "Cassegrainian" telescope, devised

by Cassegrain in 1672, which differed from it chiefly in the small

mirror being convex instead of concave (see Fig. 8 <#Fig_8>, p. 113,

"Cassegrainian"). These /direct-view/ forms of the reflecting telescope
were much in vogue about the middle of the eighteenth century, when many

beautiful examples of Gregorians were made by the famous optician, James

Short, of Edinburgh.

An adaptation of the Newtonian type of telescope is known as the

"Herschelian," from being the kind favoured by Sir William Herschel. It

is, however, only suitable in immense instruments, such as Herschel was

in the habit of employing. In this form the object-glass is set at a

slight slant, so that the light coming from the object is reflected

straight into the eye-piece, which is fixed facing it in the side of the

tube (see Fig. 8 <#Fig_8>, p. 113, "Herschelian"). This telescope has an

advantage over the other forms of reflector through the saving of light

consequent on doing away with the /second/ reflection. There is,

however, the objection that the slant of the object-glass is productive

of some distortion in the appearance of the object observed; but this

slant is of necessity slight when the length of the telescope is very great.

[Pg 115]

The principle of this type of telescope had been described to the French

Academy of Sciences as early as 1728 by Le Maire, but no one availed

himself of the idea until 1776, when Herschel tried it. At first,

however, he rejected it; but in 1786 he seems to have found that it

suited the huge instruments which he was then making. Herschel's largest

telescope, constructed in 1789, was about four feet in diameter and
forty feet in length. It is generally spoken of as the "Forty-foot

Telescope," though all other instruments have been known by their

/diameters/, rather than by their lengths.

To return to the refracting telescope. A solution of the colour

difficulty was arrived at in 1729 (two years after Newton's death) by an

Essex gentleman named Chester Moor Hall. He discovered that by making a

double object-glass, composed of an outer convex lens and an inner

concave lens, made respectively of different kinds of glass, /i.e./

/crown/ glass and /flint/ glass, the troublesome colour effects could

be, /to a very great extent/, removed. Hall's investigations appear to

have been rather of an academic nature; and, although he is believed to

have constructed a small telescope upon these lines, yet he seems to

have kept the matter so much to himself that it was not until the year

1758 that the first example of the new instrument was given to the

world. This was done by John Dollond, founder of the well-known optical

firm of Dollond, of Ludgate Hill, London, who had, quite independently,

re-discovered the principle.

This "Achromatic" telescope, or telescope "free from colour effects," is

the kind ordinarily in use at present, whether for astronomical or for

terrestrial[Pg 116] purposes (see Fig. 8 <#Fig_8>, p. 113,

"Achromatic"). The expense of making large instruments of this type is

very great, for, in the object-glass alone, no less than /four/ surfaces

have to be ground and polished to the required curves; and, usually, the
two lenses of which it is composed have to fit quite close together.

With the object of evading the expense referred to, and of securing

/complete/ freedom from colour effects, telescopes have even been made,

the object-glasses of which were composed of various transparent liquids

placed between thin lenses; but leakages, and currents set up within

them by changes of temperature, have defeated the ingenuity of those who

devised these substitutes.

The solution of the colour difficulty by means of Dollond's achromatic

refractor has not, however, ousted the reflecting telescope in its best,

or Newtonian form, for which great concave mirrors made of glass,

covered with a thin coating of silver and highly polished, have been

used since about 1870 instead of metal mirrors. They are very much

lighter in weight and cheaper to make than the old specula; and though

the silvering, needless to say, deteriorates with time, it can be

renewed at a comparatively trifling cost. Also these mirrors reflect

much more light, and give a clearer view, than did the old metallic ones.

When an object is viewed through the type of astronomical telescope

ordinarily in use, it is seen /upside down/. This is, however, a matter

of very small moment in dealing with celestial objects; for, as they are

usually round, it is really not of much consequence which part we regard

as top and which as bottom. Such an inversion would, of course, be[Pg

117] most inconvenient when viewing terrestrial objects. In order to
observe the latter we therefore employ what is called a terrestrial

telescope, which is merely a refractor with some extra lenses added in

the eye portion for the purpose of turning the inverted image the right

way up again. These extra lenses, needless to say, absorb a certain

amount of light; wherefore it is better in astronomical observation to

save light by doing away with them, and putting up with the slight

inconvenience of seeing the object inverted.

This inversion of images by the astronomical telescope must be specially

borne in mind with regard to the photographs of the moon in Chapter XVI


In the year 1825 the largest achromatic refractor in existence was one

of nine and a half inches in diameter constructed by Fraunhofer for the

Observatory of Dorpat in Russia. The largest refractors in the world

to-day are in the United States, /i.e./ the forty-inch of the Yerkes

Observatory (see Plate IV. <#Plate_IV>, p. 118), and the thirty-six inch

of the Lick. The object-glasses of these and of the thirty-inch

telescope of the Observatory of Pulkowa, in Russia, were made by the

great optical house of Alvan Clark & Sons, of Cambridge, Massachusetts,

U.S.A. The tubes and other portions of the Yerkes and Lick telescopes

were, however, constructed by the Warner and Swasey Co., of Cleveland, Ohio.

The largest reflector, and so the largest telescope in the world, is

still the six-foot erected by the late Lord Rosse at Parsonstown in
Ireland, and completed in the year 1845. It is about fifty-six feet in

length. Next come two of five feet, with mirrors of silver on[Pg 118]

glass; one of them made by the late Dr. Common, of Ealing, and the other

by the American astronomer, Professor G.W. Ritchey. The latter of these

is installed in the Solar Observatory belonging to Carnegie Institution

of Washington, which is situated on Mount Wilson in California. The

former is now at the Harvard College Observatory, and is considered by

Professor Moulton to be probably the most efficient reflector in use at

present. Another large reflector is the three-foot made by Dr. Common.

It came into the possession of Mr. Crossley of Halifax, who presented it

to the Lick Observatory, where it is now known as the "Crossley Reflector."

Although to the house of Clark belongs, as we have seen, the credit of

constructing the object-glasses of the largest refracting telescopes of

our time, it has nevertheless keen competitors in Sir Howard Grubb, of

Dublin, and such well-known firms as Cooke of York and Steinheil of

Munich. In the four-foot reflector, made in 1870 for the Observatory of

Melbourne by the firm of Grubb, the Cassegrainian principle was employed.

With regard to the various merits of refractors and reflectors much

might be said. Each kind of instrument has, indeed, its special

advantages; though perhaps, on the whole, the most perfect type of

telescope is the achromatic refractor.

Plate IV. Plate IV. The Great Yerkes Telescope
Great telescope at the Yerkes Observatory of the University of Chicago,

Williams Bay, Wisconsin, U.S.A. It was erected in 1896?7, and is the

largest refracting telescope in the world. Diameter of object-glass, 40

inches; length of telescope, about 60 feet. The object-glass was made by

the firm of Alvan Clark and Sons, of Cambridge, Massachusetts; the other

portions of the instrument by the Warner and Swasey Co., of Cleveland, Ohio.

(Page 117 <#Page_117>)

[Pg 119]

In connection with telescopes certain devices have from time to time

been introduced, but these merely aim at the /convenience/ of the

observer and do not supplant the broad principles upon which are based

the various types of instrument above described. Such, for instance, are

the "Siderostat," and another form of it called the "C?lostat," in which

a plane mirror is made to revolve in a certain manner, so as to reflect

those portions of the sky which are to be observed, into the tube of a

telescope kept fixed. Such too are the "Equatorial Coudé" of the late M.

Loewy, Director of the Paris Observatory, and the "Sheepshanks

Telescope" of the Observatory of Cambridge, in which a telescope is

separated into two portions, the eye-piece portion being fixed upon a

downward slant, and the object-glass portion jointed to it at an angle

and pointed up at the sky. In these two instruments (which, by the way,

differ materially) an arrangement of slanting mirrors in the tubes

directs the journey of the rays of light from the object-glass to the
eye-piece. The observer can thus sit at the eye-end of his telescope in

the warmth and comfort of his room, and observe the stars in the same

unconstrained manner as if he were merely looking down into a microscope.

Needless to say, devices such as these are subject to the drawback that

the mirrors employed sap a certain proportion of the rays of light. It

will be remembered that we made allusion to loss of light in this way,

when pointing out the advantage in light grasp of the Herschelian form

of telescope, where only /one/ reflection takes place, over the

Newtonian in which there are /two/.

It is an interesting question as to whether telescopes can be made much

larger. The American astronomer, Professor G.E. Hale, concludes that the

limit of refractors is about five feet in diameter, but he thinks that

reflectors as large as nine feet in diameter might now be made. As

regards refractors[Pg 120] there are several strong reasons against

augmenting their proportions. First of all comes the great cost.

Secondly, since the lenses are held in position merely round their rims,

they will bend by their weight in the centres if they are made much

larger. On the other hand, attempts to obviate this, by making the

lenses thicker, would cause a decrease in the amount of light let through.

But perhaps the greatest stumbling-block to the construction of larger

telescopes is the fact that the unsteadiness of the air will be

increasingly magnified. And further, the larger the tubes become, the
more difficult will it be to keep the air within them at one constant

temperature throughout their lengths.

It would, indeed, seem as if telescopes are not destined greatly to

increase in size, but that the means of observation will break out in

some new direction, as it has already done in the case of photography

and the spectroscope. The direct use of the eye is gradually giving

place to indirect methods. We are, in fact, now /feeling/ rather than

seeing our way about the universe. Up to the present, for instance, we

have not the slightest proof that life exists elsewhere than upon our

earth. But who shall say that the twentieth century has not that in

store for us, by which the presence of life in other orbs may be

perceived through some form of vibration transmitted across illimitable

space? There is no use speaking of the impossible or the inconceivable.

After the extraordinary revelations of the spectroscope?nay, after the

astounding discovery of Röntgen?the word impossible should be cast

aside, and inconceivability cease to be regarded as any criterion.

[8] <#FNanchor_8_8> The principle upon which the telescope is based

appears to have been known /theoretically/ for a long time previous to

this. The monk Roger Bacon, who lived in the thirteenth century,

describes it very clearly; and several writers of the sixteenth century

have also dealt with the idea. Even Lippershey's claims to a practical

solution of the question were hotly contested at the time by two of his

own countrymen, /i.e./ a certain Jacob Metius, and another
spectacle-maker of Middleburgh, named Jansen.


[Pg 121]



If white light (that of the sun, for instance) be passed through a glass

prism, namely, a piece of glass of triangular shape, it will issue from

it in rainbow-tinted colours. It is a common experience with any of us

to notice this when the sunlight shines through cut-glass, as in the

pendant of a chandelier, or in the stopper of a wine-decanter.

The same effect may be produced when light passes through water. The

Rainbow, which we all know so well, is merely the result of the sunlight

passing through drops of falling rain.

White light is composed of rays of various colours. Red, orange, yellow,

green, blue, indigo, and violet, taken all together, go, in fact, to

make up that effect which we call white.
It is in the course of the /refraction/, or bending of a beam of light,

when it passes in certain conditions through a transparent and denser

medium, such as glass or water, that the constituent rays are sorted out

and spread in a row according to their various colours. This production

of colour takes place usually near the edges of a lens; and, as will be

recollected, proved very obnoxious to the users of the old form of

refracting telescope.

It is, indeed, a strange irony of fate that this very[Pg 122] same

production of colour, which so hindered astronomy in the past, should

have aided it in recent years to a remarkable degree. If sunlight, for

instance, be admitted through a narrow slit before it falls upon a glass

prism, it will issue from the latter in the form of a band of variegated

colour, each colour blending insensibly with the next. The colours

arrange themselves always in the order which we have mentioned. This

seeming band is, in reality, an array of countless coloured images of

the original slit ranged side by side; the colour of each image being

the slightest possible shade different from that next to it. This strip

of colour when produced by sunlight is called the "Solar Spectrum" (see

Fig. 9 <#Fig_9>, p. 123). A similar strip, or /spectrum/, will be

produced by any other light; but the appearance of the strip, with

regard to preponderance of particular colours, will depend upon the

character of that light. Electric light and gas light yield spectra not

unlike that of sunlight; but that of gas is less rich in blue and violet
than that of the sun.

The Spectroscope, an instrument devised for the examination of spectra,

is, in its simplest form, composed of a small tube with a narrow slit

and prism at one end, and an eye-piece at the other. If we drop ordinary

table salt into the flame of a gas light, the flame becomes strongly

yellow. If, then, we observe this yellow flame with the spectroscope, we

find that its spectrum consists almost entirely of two bright yellow

transverse lines. Chemically considered ordinary table salt is sodium

chloride; that is to say, a compound of the metal sodium and the gas

chlorine. Now if other compounds of sodium be experimented with in the

same manner, it will soon be found that these two yellow lines are

characteristic of sodium when turned into vapour by great heat. In the

same manner it can be ascertained that every element, when heated to a

condition of vapour, gives as its spectrum a set of lines peculiar to

itself. Thus the spectroscope enables us to find out the composition of

substances when they are reduced to vapour in the laboratory.

[Pg 123]

Fig. 9. Fig. 9.?The Solar Spectrum.

[Pg 124]

In order to increase the power of a spectroscope, it is necessary to add
to the number of prisms. Each extra prism has the effect of lengthening

the coloured strip still more, so that lines, which at first appeared to

be single merely through being crowded together, are eventually drawn

apart and become separately distinguishable.

On this principle it has gradually been determined that the sun is

composed of elements similar to those which go to make up our earth.

Further, the composition of the stars can be ascertained in the same

manner; and we find them formed on a like pattern, though with certain

elements in greater or less proportion as the case may be. It is in

consequence of our thus definitely ascertaining that the stars are

self-luminous, and of a sun-like character, that we are enabled to speak

of them as /suns/, or to call the sun a /star/.

In endeavouring to discover the elements of which the planets and

satellites of our system are composed, we, however, find ourselves

baffled, for the simple reason that these bodies emit no real light of

their own. The light which reaches us from them, being merely reflected

sunlight, gives only the ordinary[Pg 125] solar spectrum when examined

with the spectroscope. But in certain cases we find that the solar

spectrum thus viewed shows traces of being weakened, or rather of

suffering absorption; and it is concluded that this may be due to the

sunlight having had to pass through an atmosphere on its