2 \ ;.;,;: THE STRUCTURE OF 



jtheir, various parts were related to each other. The 

 Micropeope has 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 so 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 in two ways ; first by 

 enabling the human eye to be brought more closely 

 in contact with an object than it otherwise could be, 

 and secondly by magnifying the object looked at. 



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 only the larger letters ; 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, we could yet, by the aid of a lens a 

 piece of concave or convex glass, bring our eyes 

 nearer to the letters, and see. 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 the 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 pos- 

 sible to an object, it becomes convenient to use 

 more than one lens in a glass through which we 

 look. When these lenses are fixed in a brass tube, 



