114 HOW TO SEE WITH THE MICROSCOPE. 



It is obvious also that, if the one-sixth and the one- 

 tenth are more than capable of doing the work formerly 

 set apart for the employment of the one-fiftieth, the 

 former have the better right tp be regarded as "high 

 powers." 



Furthermore it occurs in the present advanced stage 

 of optical science that it is really quite impossible to 

 precisely define what constitutes a " medium power " 

 glass, or for what particular class of work would such 

 glasses (if defined) be characteristically adapted. The 

 ^author confidently believes that still further and greater 

 improvements in American objectives are yet to be ac- 

 complished. He believes, too, confidently that, as the 

 instrument shall approach perfection, and still higher 

 ye-pieces be brought into requisition, he may yet live 

 to see the Nobert nineteenth band with a half-inch ob- 

 jective and a one-sixteenth eye-piece. It therefore 

 seems to him that any discussion as to the characteristic 

 duties of an object-glass based entirely on the focal 

 length of the same may wisely be dismissed as being 

 (for the present at least) impractical, if not impossible. 



And now for some remarks that are not only possible, 

 but can, if the reader elects, be made eminently practical, 

 closely related, too, to what has just been written; and 

 in these the author hopes to render some service at 

 least to a portion of his readers. 



A fine objective is in its very nature a costly instru- 

 ment, while on the other hand, it often happens that 

 the true lover of nature has unfortunately a light purse. 

 In fact, this whole situation is to be regretted, and cer- 



