THE Museum has recently acquired a small collection of manuscript and printed material from the descendants of the Dollond family of optical instrument makers. A number of generations of the Dollonds are represented, reaching back as far as the founding of the company in the eighteenth century and, indeed, even further. These papers are in addition to the Dollond family papers already in the Blundell Collection, previously on loan to the Museum and now transferred as a gift.
There are a number of interesting documents in the collection but one unexpected find is of outstanding importance for the history of optical instruments. It is the original manuscript of the rebuttal prepared by Peter Dollond to Jesse Ramsden’s charge that John Dollond took the idea of the achromatic telescope from the previous work of Chester Moor Hall, having learnt of it through an encounter with the optician George Bass. It adds significantly to our knowledge of this crucial episode in the history of the telescope.
H. C. King’s History of the Telescope is still the most comprehensive account of the dispute and it relies heavily on a paper by Ramsden, also preserved at the Royal Society. King does not make clear how this paper fits into the continuing argument between Dollond and the opticians challenging the legitimacy of his patent. The newly-discovered manuscript, however, is a response to Ramsden’s communication and is headed ‘An answer to a paper presented to the Royal Society by Mr Jesse Ramsden F. R. S. which was read the 18th of June 1789 intitled remarks on a paper relating to the invention of the achromatic Telescope’. This allows us to establish the sequence of exchanges more clearly.
In the 1760s Peter Dollond successfully sued several instrument makers for infringing his patent, and in 1764 he had to mount a legal defence against a petition to the Privy Council signed by thirty-five London opticians. They claimed that the true inventor had been Chester Moor Hall, working as early as 1729, and that such telescopes had been widely made in London before Peter Dollond began to enforce his patent. They cited George Bass making achromatic lenses in 1733 and claimed that Robert Rew had been Dollond’s informant in 1755. The petition did not succeed.
These experiences made Peter Dollond vigilant and in 1789 he chose to respond, in a paper to the Royal Society, to some remarks made by Lalande, Fuss and Cassini, which he thought belittled the contribution made by his father. Though it was read to a meeting on the 21st May, as the Royal Society’s Journal Book confirms, the Society refused to print this contentious paper in the Philosophical Transactions, and Dollond arranged its publication himself.
We know that Ramsden was present when Dollond’s paper was read, for it is recorded that he introduced Giuseppe Piazzi on that occasion as a ‘stranger’. It was in response to Dollond that Ramsden placed on record at the Royal Society ‘Some Observations on the Invention of Achromatic Telescopes’ (Royal Society Letters and Papers, IX, no. 138), which was read at a meeting on the 18th June. Ramsden unequivocally states that Hall was the person ‘whom I have always been accustom’d to consider as the first Inventor of ye Achromatic object glass.’
Having received an order for a reading glass, Dollond went to buy one from Bass. He was about to choose one of flint glass when Bass advised him that more coloured fringes would be seen when using the outer parts of that lens than if he were to take one of crown glass. Ramsden, who married Peter Dollond’s sister in 1766, says that he heard about the conversation from Dollond himself.
The point of the story was that Bass’s remarks suggested to Dollond that different glasses had different dispersive powers, but Ramsden also said that Bass went on to tell Dollond about the work he was doing for Hall. Ramsden claimed further that John Bird had made a successful achromatic telescope for Hall.
Peter Dollond, who unlike Ramsden was not a Fellow of the Royal Society, attended the next meeting (on the 25th June), being introduced by Nevil Maskelyne, and the one following (on the 2nd July), when he was introduced by Edward Nairne. Ramsden’s attendance would not be recorded unless he introduced a guest. It must have been around this time that Dollond was deciding whether and how he should respond to Ramsden, and after the usual summer recess, his answer was read on the 12th November.
The substance of Ramsden’s paper is accurately summarized, despite Dollond’s caveat that, ‘I may not perhaps have been very accurate in what I have stated from Mr Ramsden’s paper because I am obliged to do it from memory, being prevented by the general usage of the Royal Society from procuring a copy’. Dollond explains that Ramsden does not contradict the points he had made with respect to foreign authors, ‘but endeavours to prove that Mr Dollond himself was not the inventor, it having been first discovered by Mr Chester Moor Hall Esqr.’ ‘Mr’ has been crossed through on the addition of ‘Esqr’.
This led him to try to make an achromatic object-glass using a doublet of water and glass, without success. He suspected that a variation in dispersive power would also be evident in different types of glass, encouraged by the fact that ‘it began to be known at that time that object glasses made of crown glass performed better than those made of common plate glass, which had been the kind generally used.’
Now writing some thirty years after the event, Peter Dollond remembered discussing the matter with his father on his return:
Peter said that John told a number of people about this, including Ramsden, ‘who at that time was almost continually at our house getting all the information he could both in the theory and practice of opticks’. Ramsden was apprenticed to Mark Burton, who was not able to satisfy his curiosity.
Peter Dollond emphasized that Bass’s remark had been nothing more than ‘a piece of information’ that had encouraged his father to pursue the experiments he had already begun with more speed and greater confidence. The most he was prepared to admit was that the encounter had brought a successful result forward by a few months. Bass’s observation was one he made to anyone purchasing a reading glass, with neither he nor they appreciating its significance. What set John Dollond apart from the rest was natural philosophy: ‘He [Bass] did not know that such a difference in the quality of two kinds of glass could be applied to any advantage. Mr Bass was a practical optician; not a theorist.’
Peter Dollond goes on to deal with the legal challenge from the opticians, and the evidence given at the time by Bass and Hall, who both declined to suggest that Dollond had acquired his invention from them.
What of John Bird? Dollond finds it impossible to say whether he had made an achromat for Hall, but he is sure that any such attempt would have had disappointing results. Bird’s opinion in the patent case that Dollond’s specification was insufficient is dismissed – ‘he was a mathematical instrument maker and perhaps did not understand much of opticks’ – and no object glasses he could have made for Hall would have encouraged further development.
The concluding paragraph of the Museum’s manuscript identifies the ground for the dispute between Dollond and Ramsden. Peter Dollond thought that his brother-in-law was making a distinction between Dollond’s legal rights, established through the confirmation of his patent, and the ‘philosophical’ (meaning here ‘natural philosophical’) credit, which Ramsden assigned elsewhere. Dollond, who thought the matter had already been settled by law, responded, as we have seen, by claiming that philosophical legitimacy belonged to his father, but he also wanted to reject the distinction that Ramsden had made:
In fact his reply was already on record at the Royal Society. There and in the manuscript in Oxford are preserved John Dollond’s account, related through his son, of his meeting with George Bass, and of his otherwise unrecorded meeting with Chester Moor Hall.