68 Immersion Lenses and New Uefradometers. 



writer in the ' Ency. Brit.,' gives the artist a wider range in his 

 experimental researches." M. Achille Brachet, of Paris, has added, 

 in Itahan, M. Amici's own account of his invention. 



" These glasses were constructed on a new principle — that of 

 immersion in water — and the most extraordinary point of the dis- 

 covery was the very considerable distance preserved between the 

 objective and the object under view." 



" The series No. III. and No. VI. on this new principle renders 

 the image more clear and distinct, and does not require any correc- 

 tion of the error which the common system introduces, owing to 

 the different thickness of the covering glass. This advantage was 

 obtained by immersing in a drop of distiUed water the last lower 

 surface of the series III. and VI." 



" Professor Amici is of opinion that no object-glass hitherto 

 constructed has a power as great as his Series No. VI., and con- 

 sidering the distance (about 0™™'4, or 16 thousandths of an inch)* 

 which is left between the object-glass and the object, with a large 

 aperture of 160°, he thinks he has given proof of the superiority of 

 the principle he has invented." (^V usually requires a " cover " 

 only 4 thousandths thick • 004".) " Professor Amici tells us that 

 his object-glass No. III. is composed of jive, and No. VI. with six 

 different refractive and dispersive substances." f 



The Enghsh, with their stolid resistance to change and new ideas, 

 had persisted, up to a very recent date, in ignoring the immersion 

 principle. Indeed, none of our opticians have taken them up till 

 compelled by the pressure of public opinion and ardent amateurs. 

 The splendid abilities of Professor Amici, aided by his optical 

 knowledge, perhaps surpassed herein even Andrew Eoss, who had 

 a lifetime to learn the Microscopic Art. There are even now, I 

 believe, no dry objectives made of the Y'4th of an inch focus, capa- 

 ble of viewing an object through a glass cover one-hundredth of an 

 inch thick without adventitious aid. 



Such, then, being the history of the immersion lens, our Con- 

 tinental friends, who crowded to Paris in 1855, became thoroughly 

 acquainted with the superiority of the immersion principle, and 



* A simple method of converting millimetres into inches, sufficiently near, 

 is to multiply the mm by 4 and divide by 100, or cut off two ciphers, 

 t ' Ency. Brit.,' p. 783, Ed. 1857, art. " Microscope." 



