65 



agency which, eliminating the personal factor of 

 efficiency, will give, under all conditions, results 

 closely equal to those under which the objectives were 

 originally corrected. 



"It is surprising to see how little attention is paid to 

 this subject in the large majority of standard works 

 on the microscope. Almost all books give carefully 

 prepared illustrations and descriptions showing the 

 effect on the course of light by the interposition 'of 

 the cover-glass, and after giving conclusive evidence 

 of its disturbing influence, still, in a general way, say 

 it is of little moment. 



" With such statements to guide the microscopist, 

 it is not surprising that the subject should have 

 received so little attention, and that any efforts to lead 

 to improved methods of manipulating objectives 

 should have almost completely failed because of a 

 lack of the true understanding of their need and con- 

 sequent failure to create interest. The belief is quite 

 general that any time devoted to this subject is wasted 

 and might better be utilized in other directions. I 

 hope to be able to show that this is entirely wrong, 

 and may here say that, while I may be considered an 

 extremist in the other direction, my efforts emanate 

 from the desire to put it in the power of every micro- 

 scopist to obtain the highest possible results from his 

 optical battery and equal to those obtainable by the 

 optician. 



"Outside of the differences of the lengths of tubes 

 used by different makers, which is also of great bear- 



