MAGNIFYING POWER AND MEASUREMENT OF OBJECTS 1 



also be found that even the various parts of a simple histological 

 element like a cell cannot be seen sharply with a single focal 

 adjustment. The forefinger and thumb of one hand must be kept 

 constantly on the milled head of the fine focusing -screw. Sup- 

 posing the light to be 011 our right, we devote the right hand to 

 the focusing. 



The left hand will be engaged with the glass slip upon which 

 the object has been mounted. The forearm resting upon the table, 

 let the thumb and forefinger rest on the left upper side of the 

 stage, just touching the edges of the glass slip. The slightest 

 pressure will then enable you to move the slip smoothly, steadily, 

 and delicately. 



Proceed to examine the object with method. Suppose a section 

 of some tissue to be under examination say one -fourth of an inch 

 square. With the high -power you will be able to see only a small 

 fraction of the area at once. Commence at one corner to observe, 

 and, with the left hand, move tfre object slowly in successive 

 parallel lines, preserving the focus with the right hand, until the 

 whole area of the section has been traversed. 



Practice will soon establish perfect co-ordination of the move- 

 ments involved, and will result in the ability to work with ease, 

 celerity, and profit. 



CONSERVATION OF THE EYESIGHT 



The beginner should not become accustomed to the use of one 

 eye alone, or of closing either in microscopical work. It will 

 require but little practice to use the eyes alternately, and the 

 retinal image of the unemployed eye will soon be ignored and 

 unnoticed. 



MAGNIFYING POWER AND MEASUREMENT OF OBJECTS 



The microscope is not, as the beginner usually supposes, to be 

 valued according to its power of enlargement or magnification, 

 but rather according to the clearness and sharpness of the 

 image afforded. 



Magnifying power is generally expressed in diameters. A 

 certain area is by the instrument made to appear, say, ten times 

 as large as it appears to the naked eye. This object, then, has its 

 apparent area increased one hundred times; but reference is made 



