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The reflecting telescope and James Short
James Short described himself as an ‘optician solely for reflecting telescopes’ (Bryden, 1969; Clarke, 2006; Turner, 1969). A public avowal of that degree of specialism in the instrument trade was very unusual in eighteenth-century London. Makers who offered their wares in shops supplying retail customers were more inclined to maximise their apparent range, even though there surely were very specialised workmen either in the workshop behind the shop or, more likely, in the workshop of a subcontractor supplying parts or processes. Yet it was usual to give customers the impression of a business boasting a wide range of instruments. So how did Short come to be, in public, an optician solely for reflecting telescopes?
To understand this we have to go back to Newton’s account of his design for a reflector in the first edition of his Opticks of 1704, where he emphasises that he made his own telescopes – grinding and polishing the metal mirrors by hand. While he goes through the process in detail, he also makes the point that communication in words is of limited use: ‘This Art of polishing will be better learnt by repeated Practice than by my description’ (Newton, 1704, p 77).
Newton offers two contexts for proposing a shift from the refractor to the reflector. The one generally emphasised by historians is his tenet that colours are not created by the process of refraction: they pre-exist in the incident light and their different refractive properties mean that refraction inevitably results in their dispersion. Thus, dispersion into colours is unavoidable when light passes through a lens. Furthermore dispersion for a given degree of refraction is the same for all types of glass, so there can be no possibility of recombining the colours to give a resultant deviation without dispersion, and so a refracting telescope can never be perfected so as to give a truly sharp image.
Seeing therefore the Improvement of Telescopes of given lengths by Refractions is desperate; I contrived heretofore a Perspective by reflexion, using instead of an Object Glass a concave of Metal. (Newton, 1704, p 75)
Newton also presents his telescope construction under the title ‘To shorten telescopes’, that being an obvious desideratum of contemporary telescopic astronomy with its very long refractors. The combination of lenses and mirrors to shorten telescopes was also a concern of Robert Hooke, who had a telescope 60 feet in length, and both his and Newton’s designs were regarded as ‘catadioptrical’ instruments, rather than, at this stage, ‘reflecting’ telescopes, because they used combinations of mirrors and lenses (Bennett, 2006). The upshot of this work was that Newton’s legacy to the development of telescopic optics in Britain was a perhaps unexpected combination of geometrical and artisanal practice: practitioners analysed the geometry and the natural philosophy of the properties of light, but they also worked at making metal mirrors.
Given the character and content of Newton’s Opticks, the composition of the great Newtonian optical treatise of the eighteenth century by the Cambridge mathematician Robert Smith – his Opticks of 1738 – is, for the most part, unsurprising (Smith, 1738). It is organised into four ‘books’, denominated ‘popular’, ‘mathematical’, ‘mechanical’ and ‘philosophical’. ‘Mechanical’, referring to the design, manufacture and use of instruments, might be expected, but this is a very early use of ‘popular’ to describe an introductory scientific text for a general, non-specialised public. Newton’s Opticks was certainly mathematical, mechanical and philosophical, but it was hardly popular, despite being the most accessible of his books. Yet a popular culture of optics had begun to develop in the early decades of the century and Smith’s book would give it further impetus. A great many serious amateurs in astronomy and telescope-making began with Smith or encountered him at an early stage, while, increasingly, less committed participants had other resources to turn to in popular books, lecture series and instruments aimed at non-astronomers.
It was the instrument makers, rather than the mathematicians such as Smith, who further promoted this cultural and commercial opportunity. It was they who provided even more popular books and who sold the appropriate telescopes, for the most part Gregorian reflectors. The larger apertures possible with reflectors fitted them for viewing the Moon or Saturn in greater detail, or for marvelling at the variety of nebulae or clusters of stars, while the Gregorian had the intuitive advantage over the Newtonian that the observer was looking towards the object of interest. Rather than using the word ‘popular’, these authors were inclined to signal a general interest by offering their work to ladies as well as gentlemen: examples include James Ferguson’s An easy introduction to astronomy, for young gentlemen and ladies and Benjamin Martin’s The Young Gentleman and Lady's Philosophy.
While certain instrument makers indulged in quasi-academic activity, such as writing textbooks, devising courses and giving lectures, more learned astronomers rolled up their sleeves and applied themselves to grinding and polishing. Smith describes these mechanical procedures in detail, presenting this as a polite occupation, appropriate to the rational gentleman. He can cite the activity of John Hadley, Vice-President of the Royal Society, James Bradley, Savilian Professor at Oxford, and Samuel Molyneux, a member of parliament and a privy counsellor from a family of Irish gentry. If it seems unexpected to find such men working by hand in casting, grinding and polishing, we might add that their methods were being published by the Plumian Professor in Cambridge, who would shortly become Master of Trinity College and Vice-Chancellor of the University. The legitimation for all this manual work was Newtonian.
Where are we to place James Short in this context? Born in Edinburgh in 1710 into an artisanal family, he was orphaned at an early age and was accepted into George Heriot's Hospital as a pupil at the age of ten, moving to the Royal High School at 12 and eventually matriculating at the University of Edinburgh at 16 (Clarke, 2006). An early biography says he had already shown talents in handcraft – that is, in making things – and in the classics, and in the University he took to mathematics, giving up all former thoughts of the ministry. He attracted the attention, support and patronage of Colin MacLaurin, Professor of Mathematics, who was a follower and friend of Newton; indeed, MacLaurin had been appointed to succeed the Newtonian David Gregory to the Edinburgh chair with the help of Newton’s patronage.
© Royal Observatory Edinburgh
A portrait of James Short, Scottish optician, (1710-1758)
The question of the practicality of Newtonian reflecting telescopes had been under trial at the Royal Society, with Newton in the chair as President, in the early 1720s and now MacLaurin accommodated Short’s efforts to further this work in his own rooms at the University. Short worked mostly on Gregorians and, when MacLaurin wrote to Smith in 1734 of his success, Smith published the account in his Opticks. Short could hardly have had a more propitious introduction to the world of practical optics. He became a Fellow of the Royal Society on a visit to England in 1737 and he had a substantial reputation and a successful business by the time he moved his operations permanently to London in 1738, though he would always maintain his links with Edinburgh, where he visited regularly.
MacLaurin was a friend of James Douglas, Lord Aberdour, later Earl of Morton, an Edinburgh natural philosopher, who had himself become FRS just four years before Short. Douglas also became an early patron of Short’s, appointing him tutor to his children, and owning some of his telescopes. Short went with Morton to Orkney in 1739 on a surveying project, not only surveying Morton’s lands, but also working on determining the length of a degree of latitude.
Short managed to prosper in both business and scientific prestige. He became an active Fellow of the Royal Society, was called on for reports on various technical matters, published papers in the Philosophical Transactions, and operated a private observatory in his premises in Surrey Street. He served on the Council of the Society and his being in trade, as other important makers would find, did not prevent him from reaching a respected position in the London scientific world. The Newtonian basis of his craft was helpful in cultivating his position and I have suggested elsewhere that the trade description he adopted of ‘optician solely for reflecting telescopes’ could have been more than a mere statement of fact, but an assertion of his standing in the world of mathematical natural philosophy (Bennett, 2006, p 259). He died a wealthy man in 1768, leaving a fortune of about £20,000.
Component DOI: http://dx.doi.org/10.15180/140209/003