346 



[On. X 



With the horizontal microscope, unless one uses a table with a 

 drawing shelf (fig. 187), the microscope must be raised on a block 

 or support of some kind and clamped to the block so that it will be 

 rigid (fig. 193-194). A convenient height is 250 mm. (10 inches). 



To vary the magnification slightly, the distance can be made 

 greater by using an additional block, or it may be made less by 

 raising the drawing surface. For a very convenient arrangement 

 for changing the elevation of the microscope see fig. 198, 2oiC. 



For obtaining the scale or magnification of the drawing see 

 508-510. 



497. Getting the light through the horizontal microscope 

 with the plane mirror. The simplest method is to place the lamp 



FIG. 193. DRAWING WITH THE MICROSCOPE IN A DARK ROOM. 



In the arrangement here shown the light is from a small arc lamp drawing 

 current from the house lighting system. 



The supply cable and the lamp socket are shown, then the separable attach- 

 ment plug and the supply wires with the rheostat inserted along one wire (fig. 

 1 88). 



The arc lamp is at the level of the microscope mirror and at right angles with 

 the microscope axis. The light from the arc lamp is reflected up to the sub- 

 stage condenser by the mirror and passes on through the specimen and micro- 

 scope as shown in fig. 192. 



The shield between the lamp and drawing surface is to keep stray light from 

 reaching the drawing surface. The shield is represented as transparent. It 

 was left in place during only a part of the time of the exposure in making the 

 photographic negative. 



