APPENDIX. 



(Reprinted from "The Microscope," Jan., 1885.) 



CONSIDERATIONS IN TESTING OBJECTIVES. 



EDWARD BAUSCH. 



There is a laudable desire in almost all persons 

 possessing a microscope to become intimately ac- 

 quainted with it, and for this purpose it is not only 

 necessary to learn the use of its mechanical parts, 

 but to understand its optical capacity, which is .con- 

 siderably more difficult, and which involves more 

 considerations than would appear on first thought. 



With all the care which may be bestowed upon 

 objectives, they are, to a certain extent, works of 

 chance, and depend upon the optician's judgment, 

 industry and skill, and upon the variations in glass, 

 for their excellence and uniformity. These condi- 

 tions are often so varying that in the case of sev- 



