Ch. VI] DRAWING WITH A PROJECTION MICROSCOPE 185 



turn the switch on and off. A dark room is desirable, but one can 

 draw in any room at night. 



Arrange the object, the lamp, and the condenser so that the object 

 is fully hghted; then focus the objective and place the drawing surface 

 and objective at a distance apart to give the desired size of drawing. 

 Focus sharply and trace with a pencil the outlines and details which 

 it is desired to show. Finally, with the object where it can be ex- 



.-1 gJ^'^J I L- 



lock 2 Block 3 |_ Block 4 [_ 



3 



Fig. III. Projection Microscope. 

 (From Optic Projection). 



+ w The positive wire going to the upper carbon (He), and — w, wire to the 

 lower or vertical carbon (Vc) of the large arc lamp with direct current. 



Axis, Axis, Axis The principal optic axis from the source of hght (L) through 

 the condenser, the microscope and to the screen. 



W Water cell to absorb radiant heat. 



Stage The separate stage of the microscope with its water cell for cooling 

 the specimen by induction. 



Microscope In this case the microscope has an objective only; compare fig. 

 109, where an ocular is present also. 



Each element, lamp, condenser, stage, and microscope is on a separate movable 

 block (block i, 2, 3, 4) which slides independently along the optic bench or base 

 board (fig. 131). 



amined at any time, ink in the lines and details (for erect images see 

 § 282). 



§ 295. Use of a 45° mirror or a prism. — While one can draw on 

 a vertical surface it is far easier to draw on a horizontal surface. 

 This is available for all powers by using a plane mirror at 45° or a 

 drawing prism. The mirror may be at a distance from the objec- 

 tive, when it must be large (fig. 112), or it may be close to the objec- 

 tive, when it may be small (fig. 109, 114). The drawing surface 

 must be movable to vary the size of the drawing and the magnifica- 

 tion. Figures 109, .111-112 show the two principal methods of 



