2< SELECTION AND USE 



SIMPLE MICROSCOPES. 



The simple microscope is an indispensable assistant to those 

 who use the compound instrument, as well as to those who rely 

 upon it alone for the examination of flowers, seeds, minerals, 

 textile fabrics, etc. We shall therefore devote some space to 

 a consideration of its various forms, though even then we shall 

 be unable to do more than describe certain typical models 

 which, however, afford variety enough for all practical pur- 

 poses. 



Hand Magnifiers. These are so generally useful and 

 applicable that they are used by all who wish a cheap and yet 

 efficient aid to natural vision. 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 considerable 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 ex- 

 cellent form is that shown in Fig. 2. It consists of a lens of 

 1 suitable magnifying power set in a frame, which folds into a 

 case, just as the blade of a pocket knife folds into its handle, 

 thus allowing the instrument to be carried in the pocket with- 

 out liability to injury. Similar magnifiers are made with two, 

 three, and even four separate lenses, as shown in Fig. 3. The 

 lenses are usually of different powers a 2 inch, 1 inch, and 

 inch, forming a very "useful combination. Each lens may be 

 used separately, or two may be used together, or all three may 



