322 THE MICROSCOPE 



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 practice, 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 doublet of three, a triplet. All sim- 

 ple 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 simple 

 microscope. In Fig. 77, which represents the working of the 

 simple microscope, the rays from the object (a 6), passing 

 through the lens (L), form an image (a 1 b 1 ) in the retina of the 

 eye (E), and as all images are inverted in the eye, the object i? 



FIG. 77. SIMPLE MICROSCOPE 



seen as all other objects are, and appears erect. In Fig. 78 is 

 seen the action of the compound microscope. An inverted 

 image (a 1 fr') 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. 



7. A Compound Microscope consists of two portions : the 

 optical portion, or the lenses, and the mechanical portion, or 

 the instrument which bears the lenses. The glasses of a com- 



' 6. Explain, by means of the diagram, the action of the compound microscope. 

 7. Portions, in a compound' microscope ? The glasses '/ 



