OF THE MICROSCOPE. 23 



DIFFEKENT FOEMS OF THE SIMPLE MICKOSCOPE. 



To describe the different forms in market, either of simple or 

 of compound microscopes, would require a large volume. We 

 shall therefore content ourselves with a description of certain 

 typical models which afford variety enough for all practical 

 purposes. 



Hand Magnifiers. These are so generally useful and 

 applicable that no person who attempts to work much with the 

 microscope can possibly do without one. They are found in 

 market in a great variety of forms, styles of mounting, and 

 price, and are too well known to need minute description. 

 Large lenses, magnifying two or three times, are mounted 

 singly, and used chiefly for the examination of pictures, and as 

 reading glasses; the smaller sizes of the same style serve for 

 the examination of fine engravings. Very small lenses of con- 

 siderable power, and simply mounted in a frame, are also sold 

 by most opticians. They are known as "watch-charms," and 

 magnify about fifteen diameters. We have also seen a very 

 powerful magnifier mounted in a little ring attached to a pair 

 of eye-glasses. 



For the purpose of the student and naturalist, a very 

 excellent form is that which is shown as attached to the Excel- 

 sior microscope. It consists of three lenses, mounted in frames, 

 and enclosed in a case so as to be perfectly protected. Each 

 lens has a different focal length, and the three, when combined, 

 give a magnifying power of twenty-five to thirty diameters. 

 Being very portable, and possessing a variety of powers, it is a 

 favorite form of pocket microscope. 



Magnifiers composed of two or more lenses, are to be had of 

 two very distinct kinds. The lenses may either be simply united 

 in one frame, without any special adaptation to each other, or 

 the instrument may consist of two or more achromatic 

 lenses combined together in a fixed and accurately deter- 

 mined relation. Examples of the former are found in the 

 ordinary two and three lens magnifiers we have just described; 

 the latter are not so common, since they are somewhat expen- 



