242 THE APPLICATIONS OF PHYSICAL FORCES. [BOOK in. 



is only acquired after long practice, and very much depends on 

 using suitable illumination. The eye must be educated to use 

 the highest powers ; and students who wish to possess the skill of 

 their masters will do well to begin their observations by the 

 gradual use of low powers. We will also remark that, as the 



FIG. 180. English form of inclined microscope. 



greater the magnifying power, the more the light which illumin- 

 ates the object and renders it visible is divided and diffused, the 

 more necessary it is to have a .brilliant light. As a rule no higher 

 power should be used than is necessary to see any particular 



