Royal Societif, 353 



me that he was about to superintend an important glass ma- 

 nufactory : to which I replied that he ought so to do, and re- 

 commended him to undertake to instruct some one to make 

 flint and crown glass. A short time afterwards (in a letter of 

 February 10, Ibl6) he again offered me his services, stating 

 '* I have recently obtained some knowledge about making 

 glass, and have lately put it in practice by two small castings." 

 But, M. Guinand, at that time, still did not know how to pro- 

 duce glass for optical purposes. 



After the departure of M. Guinand, my friend Fraunhofer 

 made several large and excellent castings which succeeded to 

 our utmost wishes. Since his death, I have myself under- 

 taken the continuation of the manufactory of glass destined 

 for optical purposes ; and I believe that I can guarantee its 

 excellence. The object-glasses recently constructed by my 

 workmen, sufficiently well attest that the secret of making 

 flint glass, of any size, for optical purposes, is not yet lost, as 

 the Globe would have us believe. I assure you I shall be 

 happy to see our neighbours follow us, or even surpass us, in 

 an art which is so immediatel}' connected with the interests of 

 science. I shall take care, on my part, to continue the re- 

 searches commenced by fVaunhofer on the theory of light, 

 hoping that those who contribute thereto will receive the re- 

 ward which they so justly deserve. Siium cuiqtie. 



Utzschneider. 



LI. Proceedings of Learned Societies, 



nOYAL SOCIETY. 



THE following are abstracts of papers vv'aich have been read before 

 the Royal Society, during the present session. 



Mr. Lister's paper on the Compound Acliromatic Microscope of 

 Mr. Win. Tulley ; with some account of the present state of tlie mi- 

 croscope, and suggestions for its improvement on a new principle. 

 Communicated by Dr. Roget, Sec. R.S. 



The principles on which the reflecting, and also liie achromatic 

 refracting telescope are constructed, have been recently applied with 

 considerable success to the microscope, and have added much to the 

 power of that instrument. The author speaks with much commen- 

 dation of the |)eculiar construction adopted in Mr. Tulley's compound 

 achromatic microscopes, consisting of a combination of object-glasses 

 of short focus ;md large aperture, the curvatures of whicli are such as 

 very nearly to equalize the refractions produced by each. As the 

 magnitude of the ai)crturc, he observes, is valuable only in proportion 

 to that of the pencil of light which it admits, tlie latter circumstance 

 is that which chiefly claims attention ; and as it is often erroneously 

 eKtimated, a method is |)ointcd out of ascertaining it with sufficient 



N.S. Vol.7. No. 11. May 18.'}0. 2 Z exactness 



