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 satisfactory 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 



