3l6 THE SCIENCE OF MICROSCOPY. 



cope to obtain such a rational insight into the precise function of 

 its several parts as may serve to guide each in their respective 

 studies. On the other hand, the teaching of the theory of the 

 microscope is not limited to the elucidation of problems in pure 

 optics, the explanation of a lens performance, or the perspective 

 effect of light and shadow, but also suggests the means of effecting 

 improvements of the optical apparatus, and in the mode of using 

 them. The theorist who endeavours to put his principles into 

 practice is as truly a special scientist as the worker in any special 

 branch of natural science who, while affecting to consider his 

 microscope but a means to an end, does not consider the possible 

 pitfalls into which he may be entrapped by trusting solely to an 

 uninstructed instinct for the warrant of his observation. 



But if this be so, it must be an error to maintain that the 

 interest of the microscopist in the theory of the microscope is 

 exhausted as soon as the optician's work is fully accomplished, 

 or that he needs no aid from theory in gathering his harvest of 

 revelations. For how are these revelations to be verified ? How is 

 microscopic observation to be raised above mistakes of eyesight 

 exercised under unnatural conditions, and uninformed respecting 

 the principles of interepretation, in virtue of which the observation 

 ranks as a science ' And what if some of the most important 

 ''revelations" should prove to be those which in revealing the 

 peculiar actions of the microscope, with its peculiar excellencies 

 and defects, solve at the same time abstruse optical problems, or 

 bring to light subtle physical effects of matter in its minutest 

 visible particles? For the microscope itself is an illustration of 

 special optical questions, and an instrument by which physical as 

 well as anatomical analysis may be conducted. And whether our 

 research be directed to molecular physics, or organic particulate 

 form 3 to the behaviour of light interrupted by contact with matter 3 

 or to the investigation of the endlessly diverse modifications of 

 structure, we alike come to the conclusion that the microscope can 

 only be used with benefit when its revelations are verified and 



