THE SCIENCE OF MICROSCOPY. 30^ 



of observation abound even when vision is exercised in the natural 

 manner and under the most favourable circumstances, so that 

 distrust of the uncorrected evidence of our senses has become 

 proverbial, it would be a strange exception if microscope 

 "revelations" should be accepted without scrutiny or warrant, 

 other than the observer's ready faith in that which is right in his 

 own eyes. 



The microscopist is, at the very outset, placed at a disadvantage 

 of which he is frequently quite unconscious. Inferences of form 

 and structure deduced from light and shadow images, rest upon the 

 general assumption that the optical characteristics of an image 

 formed by refraction, necessarily suggest conceptions of material 

 configuration which exactly tally with objective facts. But this 

 assumption is incorrect for so large a class of objects (as also 

 instruments !) that the observer, who knows how many causes of 

 distortion of image may operate in the microscope,* will often 

 withold his judgment where the inexperienced will entertain neither 

 doubt nor suspicion. 



Another difficulty and one which pursues the microscopist from 

 the beginning to the end of his work, is that of finding settled 

 principles as well as methods of procedure in his endeavours to 

 obtain correct and constant results. As for instance, in securing 

 the perfect projection of light and shadow required for a true 

 microscope image. Supposing the instrument to be perfect, it yet 

 remains for the microscopist to give it fair play. And it is not 

 merely when examining some particularly difficult object, or testing 

 the performance of an objective that the best effect of light is 

 required, but equally so in every-day work and every kind of 

 observation. Until the microscopist understands and profits by the 

 suitable combination of lens power and illumination, which the 

 object he is about to examine demands, he will not — nor can he 



* The dioptric microscopic image is, of necessity, infinitely more liable to 

 distortion than the simple plane mirror-reflections to which we are accustomed 

 in ordinary life. 



