THE MICROSCOPE, 



MICROSCOPES may be divided into two general classes, simple 

 and compound. 



The simple microscope is used for coarse dissections of small 

 objects, and for the purpose of obtaining a general view of the 

 specimen. 



With a simple microscope we see the magnified image of the 

 object; the rays of light proceeding directly from the specimen 

 itself to the eye. 



A simple microscope may consist of but a single lens, although 

 two or more lenses are frequently employed. These lenses are so 

 arranged that they act upon the rays of light as a single lens. 



A valuable form of a simple microscope is that known as the 

 "Coddington" lens. It consists of a sphere of glass with a deep 

 groove in its equatorial part, filled with opaque matter. While 

 this opaque matter limits the central aperture, yet it allows of the 

 admission of considerable light, and gives a large field good in 

 every part. 



The "Stanhope" lens is another form of a simple microscope. 

 It differs from the "Coddington" lens in that its two convex surfaces 

 are of unequal curvatures. These surfaces are separated by a 

 quantity of glass of such a thickness, that when the more convex 

 surface is turned toward the eye, any object placed on the less con- 

 vex surface will be exactly in focus. A good "Stanhope" lens is a 

 convenient form of a pocket-magnifier, although for this purpose we 

 have not found it equal to a first-class "Coddington." 



For the small sum of two dollars one can procure a "Codding- 

 ton" lens, well mounted in brass, giving plenty of light, and having 

 a large field, suitable in every way for the office table; while for five 

 or six dollars a lens can be purchased, elegantly mounted in silver 

 or aluminum bronze, and especially adapted for a pocket-magnifier. 



3 



