4: THE STRUCTURE OF 



Simple Microscope. Of course many other things 

 may be added to it, to make it more convenient for 

 observation ; but these are its essential parts. 



But, although the Simple Microscope embraces 

 the essential conditions of all Microscopes, and has, 

 in the hands of competent observers, done so much 

 for science, it is, nevertheless, going out of fashion, 

 and giving way to the Compound Microscope. Al- 

 though this instrument is much more complicated, 

 as might be inferred from its name, than the Simple 

 Microscope, it is now constructed with so much 

 accuracy, that it can be used with as great certainty 

 and ease as the Simple Microscope itself. In order 

 to understand its construction, we must study the 

 nature of the lens of which we have been speaking. 

 If we take a lens, and hold it against an object on 

 one side, and place a piece of white paper on the 

 other side, we shall find that, at a certain point, a 

 picture of the object will be produced on the paper. 

 This is the way in which pictures are produced by 

 the camera, of which the photographic artist avails 

 himself for his portraits and sun-drawings. This 

 picture of the object, then, exists in the air at a 

 certain point beyond the lens. Now, this picture 

 may be looked at by another glass, of the same 

 character as the first ; and by this means the object; 

 is brought in a very enlarged form to the eye. 

 Now, this is the principle involved, in the Com^ 

 pound Microscope. In order to effect this object, a 

 tube (generally a brass tube) is fitted to the object- 

 glass, and at the upper part of this tube a glass is 

 fitted on, called an eye-piece. The eye-piece con^ 

 sists generally of two lenses, the object of which is 

 to bring the picture in the tube to a condition in 

 which it can be seen by the eye as readily as it 

 could through the object-glass itself. It is obvious 

 that such an arrangement as this has great advan- 



