MICROSCOPICAL DIAGNOSIS. 



The Mirror-Bar should swing with an easy and firm motion to 

 any obliquity. On some stands the mirror-bar is so arranged that 

 it can be raised over the stage for the illumination of opaque 

 objects. 



The Eye-piece "2." The one most generally used is the Nega- 

 tive or Hughenian eye-piece. It consists of two plano-convex 

 glasses, with the convex sides directed downward, and placed at a 

 distance from each other equal to one-half the sum of their focal 

 lengths. The lens nearest the eye is called the eye-glass, and the 

 one more distant from the eye and nearest the field, the field glass. 



A positive eye-piece differs from the above in that the field 

 glass has its convex surface directed upward. 



A Diaphragm is placed between the two glasses of the eye-piece, 

 in the visual focus of the eye-glass. 



A solid eye-piece is really a Stanhope lens. It gives a large 

 field and clear definition. Eye-pieces are generally lettered in this 

 country and numbered abroad. 



In lettering eye-pieces, "A" represents the lowest magnifying 

 power; hence it is known as a "low," or "shallow" eye-piece. In 

 numbering, "i" corresponds to "A." 



An "A" eye-piece then might be known as an "i 1-2 inch," a 

 "low" or "shallow" eye piece; while a "D" might be known as an 

 "1-2 inch," a "high," or a "deep" eye-piece. 



As an eye-piece magnifies the image formed by the objective so 

 will it magnify the imperfections of the objective. It must be 

 apparent, therefore, that high or deep eye-pieces should only be 

 used with the very best of objectives. 



The Objective "3." This is the most important part connected 

 with the microscope. 



Objectives are numbered according to their equivalent focal 

 lengths. Thus, by an one-fourth inch objective we mean an object- 

 ive whose magnifying power is the same as a simple lens with a 

 focal distance of one-fourth of an inch. It is a fact, however, that 

 the objectives constructed by different makers and said to be of the 

 same focal lengths, differ from each other in magnifying power to a 

 considerable extent. 



The shorter the equivalent focal length the " higher " the 

 objective, and the greater its magnifying power. 



An objective is composed of one or more systems of glasses. 



