238 THE MICROSCOPE. 



minute globule or bead, which, when set in a piece of 

 metal and used to examine objects on a plate of glass held 

 up to the light, gives a high magnifying power. In prac- 

 tice, however, it is found better to use several magnifying 

 glasses of moderate power, than a simple lens alone of 

 high power. A combination of two lenses is called a doub- 

 let of three, a triplet. All simple microscopes throw an 

 enlarged image of the object upon the retina. Compound 

 microscopes are so constructed that the enlarged image of 

 an object is again magnified by a second lens, and hence 

 their magnifying power is vastly superior to that of simple 

 microscopes. 



6. The accompanying diagrams will explain the action 

 of the compound microscope compared with that of the 



FIG. 58. SIMPLE MICROSCOPE. 



simple microscope. In Fig. 58, which represents the work- 

 ing of the simple microscope, the rays from the object (a b), 

 passing through the lens (L), form an image (a' b') in the 

 retina of the eye (E), and as all images are inverted in the 

 eye, the object is seen as all other objects are, and appears 

 erect. In Fig. 59 is seen the action of the compound 

 microscope. An inverted image (a' V) of the object (a b) 

 is magnified by the. second lens (L'), and an erect image is 

 thrown upon the retina, which, as all other objects seen 

 erect with the naked eye are inverted, gives to the image 

 a contrary direction, or inverts it to the mind. 



G. Explain, by means of the diagram, the action of the compound microscope. 



