224 M. Chevalier's Ansrcer to Dr Goring s 



resulting from colleges of mines. In my last letter I suggest- 

 ed to him the use of the protomuriate of tin, not of the nitrate 

 of copper; and in his reply he informed me that his method 

 was so simple, that he feared the workmen would deprive him 

 of the fruits of it. As the mail was closing, he postponed the 

 communication to his next letter, which, however, he never had 

 an opportunity of writing, having previously, as well as many 

 others of my able pupils, fallen a victim in the war of inde- 

 pendence. 



Should the Philosophical Society continue their liberality to 

 me, by supplying me with a fragment of the white silver glance 

 (zceisgulden of the Germans), I propose to extend my experi- 

 ments to that ore. 



Note A. — The Mexican amalgamator divides his loss of mer- 

 cury into two parts; the first he terms consumido, which is al- 

 ways equal at least to the weight of silver obtained. The 

 second termed perdida, is the waste in washing, &c. 



Art. VII. — A Letter from Charles Chevalier, Optician in 

 Paris, to Dr Goring, being an Answer to his Paper pub- 

 lished in the Second Volume of the Nezo Series of the Quar- 

 terhj Journal of Science, p. 248, entitled, " A Critique on 

 the thick Aplanatic Objcct-Glasses for divergent rays of Vin- 

 cent Chevalier aine etjils" Communicated by Dr Goring. 



Sir, 



I have read with the greatest interest the different papers you 

 have published on the microscope, and which have greatly 

 contributed to the improvement of those useful instruments. 



As vou have had the kindness to honour our labours by 

 writing an article or critique upon the achromatic object glasses 

 which we worked for Mr Lister, I hope that you will receive 

 favourably the details which I here transmit to you relating to 

 our achromatic microscopes, and which are in answer to your 

 critique, bearing date from October to January 1828, (See Dr 

 Goring's Remark A, p. 238,) in which, after having exa- 

 mined the different object-glasses of Mr Lister, you make seve- 

 ral observations, to which I reply. 



