THE KISE OF ACHROMATISM 



147 



object-glasses that we must attribute the strictly scientific value and 

 progress in development of this now extremely valuable and beauti- 

 ful instrument. An exhaustive account of the earliest discovery 

 and progressive application to our own day of achromatism, so far 

 as it can be given in this treatise, will be found in the chapter on 

 objectives. We can here only attempt, for the sake of completeness, 

 a very broad outline of the facts. 



Martin appears to have constructed an achromatic objective in 

 1759, but no results of practical value were obtained, Martin having 

 formed the judgment that his achromatic microscope was not equal 

 to a reflecting microscope with which he compared it. But it cer- 

 tainly gives him a place of interest in the history of the achromatism 

 of object-glasses for the microscope. 



FIG. 114. Ellis's aquatic microscope (1755) 



In 1762 Euler began to discuss the theory of achromatic 

 microscopes, and in 1771, in his * Dioptrica,' he entered upon the 

 subject at more considerable length. A pupil of his, named Nicholas 

 Fuss, published in St. Petersburg, in 1774, a volume entitled ' Detailed 

 instruction for carrying lenses of different kinds to a greater degree 

 of perfection, with a description of a microscope which may pass for 

 the most perfect of its kind, taken from the dioptric theory of 

 Leonard Euler, and made comprehensible to workmen by Nicholas 

 Fuss.' This was translated into German by Kliigel in 1778, but no 

 result of these discussions of the theory of achromatism can be 

 discovered earlier than 1791, when Francois Beeldsnyder made an 

 achromatic objective which was presented by Harting to the museum 

 of the University of Utrecht ; but it was far from satisfactory. It 



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