THE MICROSCOPE. 



Vol. V. ANN ARBOR, JANUARY, 1885. No. 1. 



ORIGINAL COMMUNICATIONS. 



CONSIDERATIONS IN TESTING OBJECTIVES. 



EDW. BAUSCH. 



THERE is a laudable desire in almost all persons possessing a 

 microscope to become intimately acquainted with it, and 

 for this purpose it is not only necessary to learn the use of its 

 mechanical parts, which is simple, but to understand its optical 

 capacity, which is considerably more difficult, and which in- 

 volves 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 opticians judgment, industry and skill, and upon the varia- 

 tions in glass, for their excellence and uniformity. These con- 

 ditions are often so varying that in the case of several objectives 

 of the same formula, made at the same time there will be such 

 great differences that it can hardly be perceived on the first 

 examination, that they were to be of a kind. It is at this point 

 especially necessary to detect the errors, to determine their 

 cause and apply the remedy, and to do this properly often in- 

 volves an inconceivable amount of work, and in many cases 

 the final results are reached at a pecuniary loss. There are cer- 

 tain fixed tests for each kind of objective, and to the best of 

 my knowledge all reputable opticians bring each objective up 

 to its standard before allowing it to pass their hands, irrespect- 

 ive of the cost of doing so. This must of necessity be so, if 

 only out of business consideration, and not for a love of such 

 production, for it is evident that a well-earned reputation would 

 soon lose its pre-eminence, and would acquire one for unrelia- 

 ble or poor work, if on comparison objectives of the same kind 

 would show a marked difference. There is sometimes a fortun- 



