Immersion Lewises and New Refraetomefers. 



67 



This valuable experiment of Ptolemy I particularly beg to recom- 

 mend to those opponents of immersion lenses who deny that by their 

 means a much gi-eater amount of rays radiating from a Canada- 

 balsam mounted object ultimately reaches the eye of the observer 

 than can possibly be effected by aerial or dry refraction in the 

 ordinary way.* 



In order to show the agreement between Ptolemy's Tables and 

 those given in the papers by the writer " On the Optical Advan- 

 tages of Immersion Lenses," it will be convenient to the reader to 

 reproduce here the final Table of results from page 140, September 

 Number, 1870. 



TABLE V. 



Tracing the history of immersion lenses, we may relate that Sir 

 David Brewster employed lenses recently extracted from fish and 

 other animals, as well as minute drops of castor oil, &c., formed 

 into plano-convex lenses, and even a mixture of fluids of different 

 dispersive and refractive powers, and indeed glass lenses immersed 

 in fluids. This was about 1812. 



In 1855 Professor Amici showed, at the Paris Exposition, a 

 microscope acting upon the immersion principle, which " exhibited 

 certain strife^ better than any of the instruments under examina- 

 tion " by the jurors in Class YIII. This superiority was produced 

 by the introduction of water between the object and the object-glass ; 

 but as Professor Amici could not be considered as an exhibitor, the 

 jury was not called upon to adjudicate to him a medal.| 



" The employment of fluids of various dispersive powers, says the 



* See Mr. Wenham's Paper, Jan., 1871. 



t The Ainician Test for many years held a first rank as a test for the y^^th. 



X "Mr. Andrew Ross intended to exhibit in Paris object-glasses of a still 

 higher order than those we have mentioned, and would thus have found 

 himself in competition with his eminent rivals, Messrs. Smith and Beck, and 

 M. Nachet. He was prevented, however, by the pressure of business from 

 exhibiting the new object-glass, and Messrs. Smith and Beck, who had no 

 English rival, carried oif the microscopic prize, by receiving a medal of the first 

 class. Although the microscope of M. Nachet was not equal to that of the 

 English artists, it had such a high degree of merit, that a medal of the same 

 value was adju Iged to him." — ' Ency. Brit.,' art. " INIicroscope." 



