9 2 



PRACTICAL MICROSCOPY. 



be remembered that the rays are, for all practical purposes, 

 parallel, and thereby differ essentially from artificial light, 

 the rays of which converge strongly from the luminous 

 centre. For use at home there is nothing, perhaps, so 

 convenient as an argand gas reading lamp, sliding up and 



down on a metal rod, 

 with a shade over it 

 to prevent extraneous 

 light from reaching 

 the eyes. Students 

 are very apt to work 

 with too much light, 

 and thereby impair the 

 sensitiveness of their 

 eyes ; they should 

 endeavour, however, 

 to work with only just 

 as much light as is 

 necessary to bring 

 out plainly the details 

 of the object under 

 examination, and no 

 more. 



If an oil lamp is 

 desired, a very com- 

 mon one maybe made 

 to answer almost 

 every ordinary pur- 

 pose, provided it is low enough, as when it is required to be 

 raised, that may be readily accomplished by means of 

 blocks of wood of varying thickness. The ordinary form of 

 microscope lamp is shown in Fig. 8 1 ; it differs slightly in con- 

 struction in the hands of different makers, but the student 

 should eschew all forms in which the oil reservoir case is 



FIG. 82. 



