18 MAGNIFYING POWER. 



use of the drawings; for, without it, the observer will 

 be unable to apply such a magnifying power of the 

 microscope as will enable him to see the structural 

 appearances figured in the drawings. 



The observer must also be acquainted with the 

 magnifying powers of his microscope with the various 

 object-glasses and eye-pieces. These are usually 

 given when the instrument is purchased. Or they 

 may be determined approximative^ thus : An ivory 

 scale, with y^th of an inch engraved upon it, is 

 placed on the stage, and viewed as an opake object, 

 both eyes being kept open ; and the size of the image 

 of one of the gradations is measured with compasses, 

 upon the stage as seen with that eye which is not 

 applied to the eye-piece. The number of T ^o tns f 

 an inch contained in the measure obtained with the 

 compasses represents the magnifying power. Thus, 

 supposing the image of the T ^o tn f an mcn on the 

 scale appears magnified to the length of 1 inch on 

 the stage ; the magnifying power is 100 diameters, or 

 100 times linear. This proceeding is difficult to any 

 one unaccustomed to the use of the microscope, yet 

 by practice it becomes very easy. Other methods, 

 which require the use of the camera lucida, are given 

 in the Micrographic Dictionary. 



