SUPPLEMENT 



MICROSCOPIC ILLUSTRATIONS. 



CHAPTER I. 



Memoir concerning the Verification of Microscopic Phe- 

 nomena, with fruits of experience relative to the analysis 

 of Test Objects, and the defining and penetrating powers 

 of Microscopes and Engiscopes* 



BY C. R. GORING, M.D. 



THAT there may be no disputes or mistakes concerning 

 terms or words, it is necessary to determine accurately 

 what I mean by defining and penetrating powers as dis- 

 tinct from each other. It will, I believe, be found, from 

 the consideration of various passages in my writings, that, 

 by defining power, I mean nothing more than a destitution 

 of both kinds of aberration, considered independently ot 

 the aperture of the microscope or engiscope ; and, by 

 penetrating power, merely a large angle of aperture, which 

 may or may not be associated with an aplanatic and achro- 

 matic construction. The union of these two properties 

 of course constitutes the perfection of an instrument, and 

 is, by some writers, resolved entirely into defining power, 

 which is or is not accurate, according to the sense in which 

 the word is used. As, however, by Sir W. Herschel, the 



