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Catadioptrics and Commerce in Eighteenth-Century London

The activities of instrument makers in eighteenth-century London have given historians of science opportunities to reflect on the role of commerce in the development of experimental natural philosophy. They have been less interested in professional mathematical practice, such as navigation and surveying, but professional work also was thoroughly entangled with the commerce of instrumentation. The traditional distinction between mathematical instruments, used by professional practitioners, and instruments of experimental philosophy survived well into the eighteenth century, but it did not mark an absolute separation: the telescope, for example, was important in both areas, while some prominent makers were keen to trade in both mathematical and philosophical instruments. Ifwe need to be sensitive to evolution in the categories of instruments, categories of people must also be used with caution. While they are useful and necessary, they can also be misleading. 'Gentleman' and 'tradesman', for example, are among the most familiar; they overlap but are not coincident with 'customer' and 'shopkeeper', or 'client' and 'maker'. We know already that these categories cannot fully cope with a changing pattern of life and work. Some instrument makers engage with astronomy and are admitted to the Royal Society, while others teach and publish on experimental philosophy. In certain contexts gentlemen roll up their sleeves and work at the lathe or the polishing engine. This paper deals with certain significant developments in instrumentation over several decades in the mid-century, and in particular with the introduction of the Hadley quadrant. This is an early instance where we can attribute to a theorist a mathematician, a gentleman, an FRS a design or invention that had a very powerful effect on the practice of mathematical professionals, such as navigators or surveyors. There are earlier examples, such as the Gunter rule in the seventeenth century, but they are not common. The detailed story will test some of the categories we have come to accept, and will challenge customary assumptions about this development in navigational instruments. We might begin with a basic distinction between the mathematicians of the Royal Society and the mathematical instrument makers in the workshops of London. But both groups can be differentiated further, especially the makers, some of whom were close to the Royal Society both intellectually and geographically, and some were at degrees of greater distance. 'Distance' understood literally can be a valuable parameter for enriching our understanding of instrumental commerce in London.