THE AMERICAN 



MONTHLY 



MICROSCOPICAL JOURNAL. 

 Vol. XVIII. NOVEMBER, i897- No. 11, 



On the Evolution of the Microscope. 



By Edwakd M. Nelson, 



LONDON. 

 WITH FRONTISPIECE. 



One of the means of guidance for the future is a study 

 of the errors of the past. The end will he best served 

 by (a) a through investigation of a good type of instru- 

 ment designed at some period subsequent to the intro- 

 duction of achromatism, tracing the development of its 

 various parts from the earliest times. (^) A study of 

 modern instruments, showing wherein and wliy they 

 either follow or depart from the selected type, (c) The 

 collation of other material bearing on the development 

 of modern microscopes though not falling williin the 

 limits of a and b. 



The first step, then, is the choice of a type. (1) It 

 must be that towards which the modern microscope is 

 tending. (2) It must be a permanent form. 



There is only one microscope in whi»;h both these 

 necessary conditions are to be found, and that is Powell's 

 No. 1, for it requires the slightest observation to per-, 

 ceive (1) that tiie best modern microscopes are more and 

 more conforming to that type, and (2) that it has remain- 

 ed in its present form for upwards of twenty years. 



Our first duty, then, is to describe all the causes accu- 

 paulated since the invention of the microscope, that have 



