THE SCIENCE OF MICROSCOPY. 31^ 



by greater amplification, better adjustment of brightness of image, 

 sharper definition with the lower powers, or increase of angular 

 aperture with medium amplification, &c. It might, meanwhile, be 

 supposed that with this general cry for a higher performance of the 

 microscope everyone would admit that the trial of its increased 

 efficiency on every class of objects demanded a proportionately 

 careful study of the conditions on which this higher performance 

 depended, in order that the microscopist might, by due observance 

 of them, be able to realise the best possible effects, and interpret 

 them correctly ; for it is not only in the interest of optical science 

 working for the improvement of the microscope, but even more in 

 the interest of practical microscopy itself that the limitations 

 imposed by theory upon the possible development of the micros- 

 cope and the possible extent of microscopic vision should not be 

 ■unwillingly received because vague expectations of unlimited 

 future progress are entertained. The greatest service that can be 

 rendered to the optician is to cease to demand from him what is 

 impossible of accomplishment, and to await what he may be able 

 to effect under the guidance of rational theory and such improve- 

 ment of technical procedure as he can devise. While practical 

 microscopy will gain much in ceasing to expect future marvels, 

 and in relying upon the indications which optical theory now affords 

 towards a more trustworthy observation and a more methodical 

 manipulation. 



There is indeed a separateness of aim and method in the 

 technical studies of the optician and the various practice of the 

 microscopist. But as the practical optician in seeking to construct 

 lenses which shall produce a faultless image gradually realises a 

 theory of the microscope, so the practical microscopist in seeking 

 to interpret the significance of the lights and shadows imaged 

 before him falls back upon his analysis of the image-forming 

 function. Thus from the common treasury of doctrine each draws 

 the inspiration which he needs. On the one hand it is an equal 

 acquisition to those who use and those who construct the micros- 



