244 Dr Goring's Remarks on M. Chevaliers Paper, 



sible reduction of the focus. The next he made for me was 

 of two-tenths of an inch focus, and 0.1 of aperture. The 0.933 

 was made afterwards at the suggestion of Mr Lister. 



The said 0.333 focus object-glass was, I rather think, the 

 first effective one which chanced to be made at least by design 

 and principle, for it was bottomed on proof-objects previously 

 discovered with the single miscroscope. However, I shall leave 

 it to posterity to determine this point. The triple form is evi- 

 dently that adapted to the miscroscope; for one alone well ex- 

 ecuted is capable of receiving an aperture quite sufficient for 

 all ordinary purposes, and also for shewing the majority of the 

 lined objects, which advantages it combines with a good cor- 

 rection of the oblique pencil. We do not want to be eternal- 

 ly looking at proof-objects any more than the astronomer does 

 to be perpetually observing double stars and clusters of diffi- 

 cult resolution. A telescope may be a very good and valu- 

 able instrument, though it has not the power of showing all 

 the latter bodies ; and so may a miscroscope, though it should 

 not be able to exhibit the more difficult lined objects. 



I certainly do not like triple object-glasses in combination. 

 There is a dimness in the vision of opaque objects caused 

 by the loss of light from their numerous surfaces ; but if they 

 could be made thin, and with their inner surfaces in contact 

 and cemented together, two of them would evidently be clearer 

 than three double ones, (because two additional surfaces would 

 be obliterated,) and quite as effective. Moreover, lam pretty 

 sure that a triple ohject-glass highly over-corrected for spheri- 

 city and dispersion might be combined with a common lens for 

 the purpose of increasing its power and angular aperture and 

 improving its oblique pencils, and be equal in effect to two 

 triple object-glasses of equivalent foci, with a far greater sim- 

 plicity of construction. 



The practice of piling Mount Pelion on Mount Ossa will 

 never be resorted to, unless in a case of great necessity, by a 

 real artist. 



N. What a compliment is it to the reflecting engyscope to 

 construct an achromatic refractor as nearly as possible in its 

 form, 1 y directing the rays at right angles by means of a rcc- 

 tangular prism ; and this too purely on the ground of /he al- 



