178 



THE POPULAR SCIENCE MONTHLY. 



Until full command over a microscope has been acquired, tlie most 

 contradictory and perplexing results are obtained by those who use 

 high powers in the examination of difficult objects, especially if the 

 subject is very transparent. Things examined yesterday appear quite 

 different to-day, both in form and color ; and, even while the eye is 

 still fixed upon the object, a slight change in the position of the mirror 

 will alter its appearance, or present entirely new features. 



Again, an object mounted in different mediums, or without any, 

 will present the most varied appearances, and the honest investigator 

 is thus embarrassed to decide which is tlie true form. 



1 



Fio. 2. Same Scale foccsed to show Note op Exclamation Marks. 



These complications follow the use of the instrument through all 

 its stages ; but, when the causes are well understood, the difficulties 

 are reduced to a minimum, and even turned to account in the exami- 

 nation of difficult objects. 



Great success in the use of the microscope can only be obtained 

 by the skillful manipulation of the light, and he that is not acquainted 

 with the numerous schemes, devices, and contrivances in its manage- 

 ment, might as well be in the dark ; no directions here avail, and 

 nothing but diligent and constant practice will render the student 

 efficient in this respect. 



I once stood an hour watching a leading London optician strug- 

 gling to show me the true markings of a diatom with a new object- 

 glass he had recently constructed, with which he had had no previous 

 difficulty. He at last gave up the attempt in despair. Of course, an 

 objective that has once performed a specific test will do so again. In 

 this case, the only thing in fault was the management of the light. 

 This had disgraced the object-glass, and enraged its maker. 



In contrast with the above case, I may mention the real pleasure 



