40 SELECTION AND USE 



DISSECTING MICROSCOPES. 



The term Dissecting Microscope is applied to all microscopes 

 used for working upon objects under moderate magnifying 

 powers. They are used not only for dissecting, properly so 

 called, but for the study of botany, mineralogy, etc. , as well as 

 for numerous investigations in the arts. A good microscope of 

 this kind is absolutely indispensable to those who hope to do 

 more than merely look at objects prepared by others. 



For ordinary purposes of examination, the different magni- 

 fiers previously described serve very well when merely held in 

 the hand, but their performance is greatly improved when they 

 are mounted on appropriate stands, which not only enable us 

 to adjust the focus with great accuracy, but which hold the 

 lens steadily in relation to the object, and thus prevent any 

 necessity for that constant adjustment of the eye itself, which 

 always occurs when a lens trembles, and which is so fatiguing 

 and injurious to the sight. A complete dissecting micro- 

 scope should, therefore, be furnished with stand, mirror, 

 etc., and if the student can afford it, there should be some good 

 mechanical means of adjusting the focus. The importance of 

 dissecting microscopes being generally recognized, even if the 

 instruments themselves have not come into general use, nearly 

 every manufacturer of microscopes has devised a stand of his 

 own, some of which are very complete, and as a consequence 

 very expensive. We shall, therefore, rest content with de- 

 scribing a few of the simpler forms. 



The microscopist can easily construct a dissecting microscope 

 for himself, by means of a cork and some wire, for whenever a 

 piece of apparatus is to be supported steadily, while at the 

 same time it is necessary that it should be easily moved and 

 adjusted, nothing serves so well for a temporary expedient as a 

 fine cork sliding on a smooth wire. Consequently a very 

 serviceable stand for a simple microscope is easily extemporized 



