4 THE STRUCTURE OF 



called a Simple Microscope. Of course many other 

 things may be added to it, to make it more conveni- 

 ent 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. (Fig. 1, 

 p. 5.) This instrument, as might be inferred from its 

 name, is much more complicated than the Simple. 

 Microscope, but it is now constructed with so much 

 accuracy, that it can be used with as great cer- 

 tainty and ease as the Simple Microscope itself. In 

 order to understand the mechanism of the Compound 

 Microscope we must first of all study the principles 

 on which it is constructed. If we take a common 

 convex lens and place any small object on one side 

 of it, so as to be in its focus, and then place on the 

 other side a sheet of white paper, we shall find at 

 a certain point that an enlarged picture of the 

 object will be produced on the paper ; and this is 

 the way in which pictures are formed by the 

 camera of which the photographic artist avails 

 himself for his portraits and sun-pictures. Now i^ 

 we look at this picture with another lens of the 

 same character but of somewhat less magnifying 

 power, we shall obtain a second picture larger than 

 the first, and this is the principle involved in the 

 Compound Microscope. The superiority of this 

 instrument over the Simple Microscope consists in 

 an increase of magnifying power. There is, how- 

 ever, a limit to the utility of this magnifying power; 

 for when objects are greatly magnified they become 

 indistinct. This is seen in the Oxyhydrogen and 

 Solar Microscopes, where the images are thrown, by 

 means of highly magnifying lenses, on a white sheet; 

 and, although made enormously large, their details 



