SOMETHING FURTHEK ABOUT OBJECTIVES. 11] 



bringing their favorite high-power glasses for compari- 

 son, and returning to their homes satisfied with the 

 trip, leaving the one-sixth and the tenth to encounter 

 the next comer. 



It being probable that there are others who yet re- 

 main to be convinced as to the accurary or validity of 

 the claims of the " medium powers," it may be stated 

 that at this late day the writer is no longer in a minor- 

 ity of one. Microscopists of note have studied the 

 situation, arriving at similar results. About twelve 

 months ago, Mr. John Mayall, Jr., a well-known and 

 talented microscopist of London, wrote as follows: 



" I am not going to enter into a mass of details of 

 the various trials I have made with Tolles' one-fourth 

 and one-eighth. Suffice it to say that no lenses that 

 have been in my hands have ever been so thoroughly 

 tested against the best lenses by English, French, and 

 German opticians (here Mr. Mayall presents a list of 

 seventeen recent immersion objectives by the most re- 

 nowned makers in Europe); and without reserve of 

 any kind, I say these lenses are the finest I have ever 

 seen. I affirm, then, that with cen- 



tral and oblique light on all the objects that are known 

 here as tests, Tolles carried the palm. I find, on the 

 most severe tests, there is in Tolles' lenses a better cor- 

 rection for spherical aberration, the image is more crisp 

 and clear. By difficult tests, I mean, for instance, sur- 

 rirella gemma with central light, or amphipleura pellu- 

 <cida with oblique light. I urge that 



low-anele lenses will not exhibit the definition these 



