232 M. Chevalier's Answer to Dr Goring. 



According to Mr Lister, Mr Amici abandoned in 1815 his 

 first attempts upon achromatic glasses, because they were not 

 equal to his reflecting microscopes ; and it was not till 1824, 

 after the report of M. Fresnel, that the philosopher of Modena 

 undertook this work, by adopting the system of M. Selligue 

 with regard to the superposition of object-glasses. He pur- 

 sued this idea with great success, for on the 25th May 1827, 

 he brought to France a microscope whose object-glass was 

 composed of three lenses superposed, each having about six 

 lines of foci, and a large aperture, but not cemented. This 

 instrument, united to a great magnifying power, a remarkable 

 distinctness, as well as the horizontality of the instrument, and 

 excited the admiration of both philosophers and amateurs. 



During the stay of M. Amici at Paris, Vincent and Charles 

 Chevalier exhibited in the Louvre a horizontal microscope, 

 (see Remark N,) constructed on the principles and after the 

 advice of M. Amici ; and this instrument was deemed worthy 

 of the silver medal by the central jury. 



Since that time several object-glasses have been made by 

 Tulley, Amici, and Vincent and Charles Chevalier. These 

 glasses were the subject of different memoirs or commentaries 

 by MM. Amici, Goring, Lister, Lebaillif, which have great- 

 ly contributed to bring achromatic microscopes to a high de- 

 gree of perfection ; for we can obtain in France, in Italy, and 

 in England, efficacious lenses of four lines focus. The latest 

 trials made in France have proved that it is possible to make 

 achromatic lenses of two lines focus ; and that we may even 

 hope to carry still farther the power of dioptric microscopes, 

 such, for example, as to form a compound object-glass of two 

 lenses of one and a-half line focus, or of three lenses of two and 

 a-half lines focus. We may then say after this, that in a few 

 years microscopes will be brought to the highest degree of per- 

 fection, since it is probable that we shall then have made the 

 most powerful achromatic systems. 



Charles Chevalier. 

 Paris, Quai d'Horloge, No. 69, 

 lOtf* February 1831. 



