242 Dr Goring 1 s Remarks on M. Chevalier' 1 s Paper, 



plications are so very obvious, that the credit, (if any,) which 

 may be attached to them, is scarcely worth having. 



K. It would be easy to bring forward a considerable mass 

 of evidence to prove that achromatic object-glasses for micro- 

 scopes had been repeatedly tried and abandoned in this coun- 

 try many years back ; a circumstance of which I was perfect- 

 ly aware before I employed Mr W. Tulley to construct them 

 for me. Thus, in Adams on the microscope, a work publish- 

 ed in 1787, is the following passage : " Achromatic glasses. 

 How far this invention is applicable to the improvement of 

 microscopes has not yet been ascertained ; and, indeed, from 

 some few trials made, there is reason for supposing they can- 

 not be successfully applied to microscopes with high powers; 

 so that this improvement is yet a desideratum in the construc- 

 tion of microscopes, and they may be considered as being yet 

 far from their ultimate degree of perfection." — Pp. 48, 49. 



In May 1807, the celebrated Mr Troughton employed Mr 

 W. Tulley to make him a dozen achromatics of one inch focus 

 for his astronomical circles, but rejected them as worse than 

 common lenses, on account of their bad execution. It can, 

 moreover, be most distinctly proved, that Mr Dollond has had 

 a triple achromatic of one inch focus kicking about his shop 

 for more than thirty years back. The reason that none of these 

 object-glasses were brought to perfection was because proof- 

 objects., were not discovered at the time of their fabrication, so 

 that opticians had no certain object to aim at. I am convin- 

 ced that the utility of achromatics would never have been re- 

 cognized to this day ; nor would they, except by chance, have 

 been constructed in an effective manner, had it not been for 

 my own discovery of the peculiar property of the lined ob- 

 jects. In confirmation of which, I may observe, that any dis- 

 covery of fresh proofs of still greater difficulty than those pre- 

 viously known, has been invariably found to produce fresh 

 improvements in object-glasses and microscopes in general. 

 Thus, when the brassica and podura were discovered ; opti- 

 cians immediately found themselves under the necessity of 

 extending the angular aperture of their object-glasses, and of 

 combining two or three together, in order to give them the 

 power of discerning the lines on these objects; because it was 



