156 HOW TO SEE WITH THE MICROSCOPE. 



EYE-PIECES. 



It would be a real improvement to assign to individual 

 eye-pieces their actual power expressed in inches, and to 

 dispense with the arbitrary and indefinite nomenclature 

 formerly, and, to a great extent, at present in vogue. 

 Thus, let the two-inch have the same magnifying power 

 as a simple lens of two inches focus, and similarly as to 

 the other oculars used. Messrs. Spencer, Tolles, Sidle, 

 and we believe Zentmayer, adhere strictly to this plan. 



We use principally the inch, half inch, and one-fourth 

 inch. For those oculars above the inch in power, we 

 greatly prefer the solid eye-pieces. We have also the 

 two-inch and the solid one-eighth inch. The former is 

 however, but very seldom used; in fact, in our own 

 practice, it is seldom wanted or even thought of. The 

 solid one-eighth, although not in general use, cannot be 

 dispensed with when working with sunlight illumina- 

 tion in conjunction with objectives of high balsam angles. 

 We cannot too strongly recommend that every attention 

 be bestowed as to the quality of the solid oculars, and, 

 as a rule, that they be made expressly to order. 



It occasionally happens that stands fitted with poor 

 objectives are placed in the market for sale, while to 

 accommodate the quality of the objectives the powers 

 of the oculars are let down considerably thus illus- 

 trating the truth of the well-known proverb, c'est le 

 premier pas qui coute. 



Let the purchaser look well to these points before 

 consummating an investment. 



