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.
The newly-discovered manuscript, in the hand of Peter Dollond, is a draft with many insertions and alterations. There were originally thirteen pages written on seven folded folio sheets, but one of these sheets has been lost, so that pages 11 and 12 are missing. There is a fair and complete copy in the archives of the Royal Society and it is strange that this does not seem to have attracted the attention of historians interested in the dispute over the origins of the achromatic object-glass.
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.
John Dollond's famous paper on achromatic combinations of lenses was read at the Royal Society in June 1758 and published in the Philosophical Transactions the same year. By the time of John Dollond's death in November 1761, he had been awarded the Copley Medal of the Royal Society for his invention, been elected to Fellowship of the Society, and secured patent rights over the achromatic telescope, which his son Peter then began to exploit commercially.
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.
The paper deals with what Peter Dollond saw as the increasing claims among foreign authors that the theoretical work of Euler and Klingenstierna had left little to be added by John Dollond. As King has pointed out, Dollond never recognized the work of Hall and he is not mentioned in the paper.
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.'
Ramsden's paper was King's source for the account of Hall ordering crown and flint components for an achromatic doublet separately from Edward Scarlett and James Mann, and of each of them independently sub-contracting their order to George Bass, who was thus able to discover the secret. Ramsden also explains how the idea passed to John Dollond.
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.
Dollond begins by referring to his paper of the 21st May and then to the submission by Ramsden. The draft shows him struggling to express the relationship between the two. He first writes 'Mr Ramsden in answer to this paper', then crosses through 'answer to' and substitutes 'his remarks on', and finally crosses out both the insertion and the 't' of 'this' to leave simply 'Mr Ramsden in his paper'.
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'.
Dollond rehearses Ramsden's account of the story of Scarlett, Mann and Bass, of his father's visit to Bass, and of the work done by Bird for Hall. He then gives his version of these events, beginning by placing John Dollond's work in the context of Newtonian optics, and presenting him as an experimental natural philosopher, rather than a jobbing optician such as Bass: "In the beginning of the year 1757 Mr Dollond having tried the Exp 8th Expt. of the 2d part of the first book of Newton's Opticks and by that means having discovered the new principle which was that the dissipation of the different coloured rays was not in the same proportion to the mean refraction, in water as in glass ... "
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.'
John Dollond therefore began a series of experiments on different types of glass 'and he had actually begun these experiments when the circumstance happened respecting the reading-glass mentioned in Mr Ramsden's paper.' Dollond did indeed go to Bass for a reading glass, and there he found some of white flint glass and others of plate glass (not, as Ramsden said, crown glass). When Dollond was about to take one of flint glass, the crucial exchange, as characterized by his son, went as follows: "... Mr Bass said he should [inserted: himself] prefer one made of plate glass [inserted: (not of crown as Mr Ramsden asserts)] though it were a worse colour, for the object appeared through its edges to be less tinged with the colours of the prism. Mr Dollond took one of each kind: [inserted: There was no further conversation nor was the name of Mr Hall at all mentioned that ever I understood] He asked no questions; nor was there any thing more said by Mr Bass."
Now writing some thirty years after the event, Peter Dollond remembered discussing the matter with his father on his return: "When he got home he showed me the glasses, and mentioned the remark that Mr Bass had made; and added that if the difference of the dissipation of the different coloured rays could be easily perceived in looking through the two reading glasses in that way, he had no doubt but that the difference of the dispersion of the colours in the different kinds of glass would be found much greater than he had supposed it could be and on that account he should go on with his Experiments of trying all the different kinds of glass as fast as possible."
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.'
After John Dollond had perfected the invention and applied for a patent, Bass heard about this and wrote to Hall - Peter Dollond adds an insertion at this point, 'and untill this time we had never heard of Mr Hall.' For the first time Peter now admits that Hall and his father did indeed meet: '... it was not long before he called at our house.'
The conversation took place in spring 1758, that is before Dollond's paper to the Royal Society in June. What Peter learned from his father about the meeting was that Hall said he had done 'something in the same way' thirty years earlier, but that he had found it difficult to have the lenses he needed made to his specification and that, preoccupied with his legal studies, he had let the matter drop. 'He added that he was happy to find that somebody had succeeded and that the invention was likely to become usefull.'
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: "I hope the Philosophical truth of the invention of the Achromatic Telescope by Mr Dollond will now appear to be as well established as the legal truth had already been; an ingenious distinction introduced into this subject by Mr Ramsden; a distinction however not very evident to plain minds; as truth must be the same whether it be found in Westminster Hall or in the Royal Society."
The next challenge to Dollond came the following year, not through the courts or the Royal Society, but through the press. Ramsden is generally assumed to have been the author of an article signed 'Veritas' in the Gentleman's Magazine, presenting once again the case for Chester Moor Hall. 'This article was well received', says King, 'but Dollond made no reply.'
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.
J. A. B.