It is very likely that upon leaving the sun, in which nothing is in equilibrium and where all the matter composing it drives by its various motion the spherical layer of small vortexes which is in equilibrium with the superior layers (as I mentioned while discussing the weight of the planets), it is very likely, I say, that upon leaving the sun the small vortexes, although caused by the irregular motion of the sun's parts, are constrained to arrange themselves to produce their vibrations at commensurable times, and that once this arrangement is produced or this kind of equilibrium acquired, each ray maintains the same frequency in its vibrations.