CHAPTER I 

 THE SIMPLE MICROSCOPES 



The construction and use of the simple microscope (magni- 

 fiers) undoubtedly date back to very early times. There is 

 sufficient evidence to prove that spheres of glass were used as 

 burning spheres and as magnifiers by people antedating the 

 Greeks and Romans. 



The simple microscopes of to-day have a very wide range of 

 application and a corresponding variation in structure and in 

 appearance. 



Simple microscopes are used daily in classifying and studying 

 crude drugs, testing linen and other cloth, repairing watches, 

 in reading, and identifying insects. The more complex simple 

 microscopes are used in the dissection and classification of 

 flowers. 



The watchmaker's loupe, the linen tester, the reading glass, 

 the engraver's lens, and the simplest folding magnifiers consist 

 of a double convex lens. Such a lens produces an erect, en- 

 larged image of the object viewed when the lens is placed so 

 that the object is within its focal distance. The focal distance 

 of a lens varies according to the curvature of the lens. The 

 greater the curvature, the shorter the focal distance and the 

 greater the magnification. 



The more complicated simple microscope consists of two or 

 more lenses. The double and triple magnifiers consist of two 

 and three lenses respectively. 



When an object is viewed through three lenses, the magnifi- 

 cation is greater than when viewed through one or two lenses, 

 but a smaller part of the object is magnified. 



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