MODERN INVENTIONS AND THEIR RESULTS. 11 



one to form the enlarged image of the object, 

 and which, from being nearest to the object, is 

 called the Object-glass ; while the other lens 

 magnifies that image, and, from being placed 

 between it and the observer, is called the Ocular, 

 or Eye-piece. In good Compound Microscopes, 

 a greater and more varied combination of lenses 

 is used, both for the object-glass and the eye- 

 glass ; by means of which, according to the 

 power used, any object under the glass may be 

 magnified in lineal measure from a small 

 degree up to 2000 times (or diameters) ; or, if 

 we calculate this superficially (including breadth 

 as well as length), up to 2000 x 2000, or four 

 million times. 1 



7. The Compound Achromatic Microscope, as 

 we shall presently see, is the invention of a very 

 recent period. The Single Microscope, as it 

 may be called, is nothing more than a convex 

 lens, having generally a short focal distance. 

 The earliest convex lens that we have any 

 knowledge of was brought recently from the 

 East. Among the strange fruits of Layard's 



1 To make these statements thoroughly clear, and some of 

 the succeeding illustrations fully intelligible, diagrams would 

 be necessary. 



