60 Examination of Objective Glasses of Microscopes. 



favourable to the examination of those delicate tests. For 

 the examination of globules we could not perceive any ap- 

 preciable difference between the lenses. 



I would here remark, in justice to M. Nachez, that he de- 

 serves much praise for the manner in which he has improved 

 the microscope in France without augmenting the cost of the 

 instrument ; and out of England he is undoubtedly the best 

 maker in Europe, To furnish an idea of what he has done 

 to diminish the cost of a good instrument, I will compare the 

 price of the objectives which have been the subject of the 

 experiments. 



Ross, 306 francs. 



Spencer, .... 230 ... 

 Nachez, .... 60 ... 



And what is still more, he is constantly improving his lenses, 

 without adding to their expense. 



The lower powers of these makers were examined without 

 finding any sensible difference in the defining effects of them, 

 and what little there was, was in favour of Spencer. The 

 field of the three differed ; Nachez's being the least, and 

 Spencer's the greatest. We cannot bestow too much praise 

 on our American maker for the immense progress which he 

 has made in the construction of objective lenses ; and it is to 

 be regretted that he has not chosen a better mounting for them 

 than that of Chevalier, which is very defective, and prevents 

 good glasses from showing their best effects. 



I had intended making some remarks on oblique light, 

 which has come very much in use lately in observing lines 

 and points on certain objects ; but it will be better for me to 

 defer it. I would simply remark, that much caution is 

 necessary in using it, as it will not always give correct dis- 

 tances between lines. — American Journal of Science and A rtSy 

 vol, xi., No. 32, p. 277. 



