THE MICROSCOPE. 



by organ, we must call to our aid the higher class of power. In 

 fine, a complete microscopic analysis of an individual object will 

 require that it should be viewed successively with a series of 

 gradually increasing powers. 



10. But magnifying powers, to whatever extent they may be 

 carried, will be of no avail if the image produced by the object-glass 

 be not perfectly distinct and well defined ; and it will be evident 

 upon the slightest consideration, that any minute imperfections 

 which may exist in its delineation, will be rendered more and 

 more glaring and intolerable, the higher the magnifying power 

 under which it is viewed. 



With a common magnifying glass, or simple microscope, we 

 view the object itself, and are subject to no other optical imper- 

 fections in our perception of it, than such as may arise from the 

 imperfection of the lenses through which we view it ; and since 

 with such instruments the magnifying power can never be con- 

 siderable, small defects of delineation are never perceptible. It is 

 quite otherwise, however, with the class of instruments now under 

 consideration, where magnifying powers, from 1000 to 2000 of the 

 linear dimensions, are often brought into play. 



These circumstances render it indispensable that the image of 

 the object produced by the object-glass, and viewed through the 

 eye-glass, should have the utmost attainable distinctness of de- 

 lineation ; not only as regards its outline, but also as respects the 

 most minute details of its structure and colouring. 



11. Now the solution of this problem, presented to scientific and 

 practical men the most enormous difficulties ; difficulties so great 

 as to have been regarded, by some of the highest scientific autho- 

 rities of the last half-century, as absolutely insurmountable. 

 Happily, nevertheless, the problem has been solved ; and without 

 disparagement to the great lights of science, we must admit that 

 its solution has been mainly the work of practical opticians. It 

 is true that the general principles upon which the form and 

 material of the lenses depend, were the result of profound mathe- 

 matical research, but these principles were established and well 

 understood at the moment when the practical solution of the pro- 

 blem was, by scientific authorities themselves, pronounced to be 

 all but impossible. Opticians, stimulated by microscopists and 

 amateurs, then applied themselves to the work, and by a long 

 series of laborious and costly trials, attended with many and 

 most discouraging failures, at length arrived at the production 

 of optical combinations, which have rendered the microscope one 

 of the most perfect instruments of philosophic research, and one, 

 to the increasing powers of which, we can scarcely see how any 

 limit can be assigned. 



