2 THE STRUCTURE OP 



Microscope lias thus become a necessary instrument 

 in the hands of the botanist, the physiologist, the 

 zoologist, the anatomist, and the geologist. 



Let us. then, endeavour to understand how it is 

 this little instrument has been of such great service 

 in helping on the advancement of science. Its use 

 depends entirely on its assisting the human eye to 

 see — to see more with its aid than it could possibly 

 do without it. This it does by enabling the eye to 

 be brought more closely in contact with an object 

 than it otherwise could be. 



Just in proportion as we bring our eyes close to 

 objects, do we see more of them. Thus, if we look 

 at a printed bill from the opposite side of a street, 

 we can see the larger letters only ; but if we go 

 nearer we see the smaller letters, till at last we get 

 to a point when we can see no more by getting 

 closer. Now suppose there were letters printed on 

 the bill so small that we could not see them with 

 the naked eye, yet, by the aid of a lens — a piece of 

 convex glass — we could bring our eyes nearer to 

 the letters, and see them distinctly. It would depend 

 entirely on the form of the lens, as to how close we 

 could bring our eyes to the print, and see; but this 

 great fact will be observed, that the nearer we can 

 get our eyes to the print, the more we shall see. 

 The most important part of a Microscope, then, 

 consists of a lens, by means of which ihe eye can 

 be brought nearer to any object, and is thus enabled 

 to see more of it. Magnifying-glasses and Simple 

 Microscopes consist mainly of this one element. 

 In order, however, to enable the eye to get as close 

 as possible to an object, it becomes convenient to 

 use more than one lens in a glass through which we 

 look. These lenses, for the sake of convenience, 

 are fixed in a brass frame, and attached to the 

 Simple Microscope ; when there are two lenses they 



