206 HOW TO SEE WITH THE MICROSCOPE. 



two, the two-thirds or the wide-angled inch is much the 

 superior glass ; but I value these so highly that I dread 

 to use them over the fumes of chemicals. Hence I make 

 the cheaper glass do all that I possibly can, and in this 

 kind of a way the glass is really useful to me. 



It will doubtless be observed that in changing from 

 the inch or two-thirds to the one-sixth or one-tenth I 

 make a pretty big jump. This has often occurred to 

 me, and has led to the trial of several intermediate 

 powers, resulting in every instance in my going back to 

 first principles; we are still of the notion that a No. 1, 

 four-tenths, or say three-tenths of the very highest 

 aperture possible, would be a valuable glass in the lab- 

 oratory, especially in such examinations as those of 

 urinary deposits or histological work generally, and we 

 hope before long to own just such a glass, which, if a 

 success, shall not be allowed to <k hide its light under a 

 bushel." 



In the examination of malignant growths, and in the 

 study of minute pathology generally, the aforesaid pro- 

 gramme is somewhat modified. In this line one can 

 very often make entire and satisfactoiy examinations 

 with a " medium power " glass; therefore, and princi- 

 pally for the sake of convenience, I have in reserve a 

 dry one-fourth of 100. This objective (the dry front 

 to my one-sixth) will give me nice, clean and reliable 

 views under ampliations, say from 200 to 600 or 700 

 diameters. The mechanical working of its screw collar- 

 is smooth and efficient, and the glass responds promptly 

 to any change thereof. Hence it has worked its way into 



