APPENDIX. 295 



It was only at the beginning of the present century 

 that any serious attempts were made to solve this problem 

 of applied optics. In 1816, the distinguished optician 

 Frauenhofer, of Munich, constructed a tolerably perfect 

 microscope, although it had only a low magnifying 

 power. At the meeting of the Academy of Sciences, 

 April 5th, 1824, M. Selligue, one of our most ingenious 

 mechanicians, exhibited an achromatic microscope, con- 

 structed according to his own plan by MM. Yincent 

 and Charles Chevalier. From this moment the most 

 rapid progress was made in the construction of micro- 

 scopes. In 1825, the Chevaliers, and in 1827, M. 

 Amici *, constructed instruments very superior to those 

 of their predecessors. That constructed by M. Amici, 

 more especially, excited the warmest expressions of ad- 

 miration when it was brought to Paris; but it was 

 nevertheless excelled in 1834 by that of M. C. Cheva- 

 lier. About this time, MM. Oberhaiiser and Trecourt 

 devised their platine a tourbillon, while they also im- 

 proved their lenses. A systematic competition was now 

 established between them and the Chevaliers, by which 

 science profited very considerably. Subsequently to 

 this, M. Dujardinl invented his excellent illuminating 



* M. Amici, ■who is a Professor of Physics at Modena, has 

 attached his name to several optical instruments. He has invented 

 a catoptric microscope, a new camera lucida, &c. M, Amici himself 

 constructs the glasses which he uses for his instruments, and he has 

 thus succeeded in obtaining more powerful and perfect object- 

 glasses than any of his competitors. His glasses, however, possess 

 the very serious defect of being easily affected by moisture ; and I 

 have heard of one instance in which an object-glass, that was 

 bought of the learned Professor for a thousand francs, was utterly 

 unfit for use after having been carried for some way by sea, 

 although it had actually never been employed by its owner. 



f M. Dujardin, one of the most distinguished of our naturalists, 

 is now Professor of Zoology in the Faculty of Sciences at Eennes, 

 U 4 



