200 HOW TO SEE WITH THE MICROSCOPE. 



study their objectives, and if for the sake of practice 

 only, those of their friends to which they can have 

 access. There is no time lost in this occupation ; on 

 the other hand, it will usually result in economy of 

 time. For instance, if your glass totally refuses to asso- 

 ciate with the genuine " reflex," you are hereby informed 

 that such a glass is totally unfit for any such purpose 

 as resolving the last numbers of the Moller probbe plate, 

 or for any kind of duty requiring the recognition of 

 lines as close as 80,000 to the inch. Thus, by the method 

 described you can, in less than ten or fifteen minutes 

 time, settle definitely any such question as to the capacity 

 of your object-glass. 



This matter is suggestive, and with the reader's per- 

 mission I desire to " switch off on a side track " again, 

 for we have " an ax to grind." We often, yea, almost 

 every day, hear those who regard the study of objectives 

 as one worth attention, roundly condemned by workers 

 in natural history, biology, etc. The former are said to 

 be " only diatom crackers," wlio do nothing but fool 

 away their time over difficult diatoms, and are said to 

 have angular aperture " on the brain." Now, reader, 

 when you shall be permitted to peep behind the curtain 

 as often as I have had the chance in the past (which, by 

 the way, I have improved), you will find that the very 

 gentlemen who make all this hue and cry are the very 

 ones who have been and still are " fooling away" their 

 time. You will find, as a rule, that each and every one 

 of them have their little cabinet of " difficult tests," 

 over which they spend (sub rosa) night after night in 



