MAGNIFYING POWER AND MEASUREMENT OF OBJECTS. 7 



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 the 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 movements 

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

 and profit. 



CONSERVATION OF THE EYESIGHT. 



I 



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 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 has, then, its apparent area 

 increased one hundred times ; but reference is made in describing 

 such phenomena only to amplification in a single direction. The dia- 

 meter has been increased ten times and would be expressed by pre- 

 fixing the sign of multiplication, e. g., X 10. 



A convenient unit of approximate measurement for the histologist 

 is the apparent size of a human red blood-corpuscle with a given objec- 

 tive. Thirty-two hundred corpuscles, placed side by side, would 

 measure one inch ; or, we say, the diameter of a single corpuscle is 

 the thirty-two hundredth of an inch. After considerable practice, you 

 will become accustomed to the apparent size of this object with a cer- 

 tain objective and eye-piece. This will aid in an approximate mea- 

 surement of objects by comparison, and will further give the magni- 

 fying power of the microscope. If a corpuscle appears magnified to 

 one inch in diameter, it is evident that the instrument magnifies 

 thirty-two hundred times. Should the diameter appear one-quarter 

 of an inch, the power is eight hundred; one-eighth of an inch, four hun- 



