THE MICROSCOPE 



CHAPTER I 



A SIMPLE DESCRIPTION OF THE MICROSCOPE 



The microscope is an apparatus for producing an enlarged 

 image of a small object. In its complete form it is an elaborate 

 instrument, but to understand its constrviction it may be looked 

 upon as a complex form of magnifying lens with the addition of 

 means for making delicate adjustments both for moving the lens 

 and the object and for obtaining special forms of illumination. 

 It consists primarily of three parts — the body, which carries the 

 observing lenses, the stand or framework, and the illumination 

 apparatus. 



The body (M) carries an object glass (R), which is attached to The body. 

 the object end by a standard size screw thread, and an eyepiece 

 (0), which slips loosely into the tube at the eye end in a standard 

 size fitting. It has a telescopic tube, called a draw- tube (N), for 

 varying the distance between the object glass and the eyepiece, 

 and a diaphragm (Nl) to prevent reflections from the inner sur- 

 faces of the tubes from entering the eye. 



The body and its lenses combined form the magnifying 

 apparatus. 



The object to be examined is placed on the stage (D) of the 

 microscope. The object glass if used by itself acts in the same 

 manner as a lantern lens. It throws an enlarged picture of the 

 object to a position (U) at the upper end of the body, just as a 

 lantern lens throws an enlarged picture of a small lantern slide 

 upon a white screen, but instead of its being thrown upon a 

 white screen it is thrown into space. This image is examined 

 with a magnifying lens called the eyepiece (0), by which it is 

 further magnified. If the primary image were projected upon a 

 lantern screen and one were to cut a hole in the screen and stand 

 behind it with a magnifying lens focussed upon the plane of the 

 screen, one would have the same kind of instrument as a micro- 

 scope on a large and inconvenient scale. 



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