324 PROJECTION APPARATUS FOR DRAWING [Cn. X 



FIG. 182. DRAWING WITH PROJECTION APPARATUS AND A MOVABLE 

 TABLE WITH 45 MIRROR. 



Commencing at the left : 



Supply wires to the table switch. 



From one pole of the table switch a wire extends to the binding post of the 

 upper carbon of the arc lamp. 



From the other pole of the switch a wire extends to the rheostat (R) and from 

 the rheostat to the binding post of the lower carbon. 



Arc lamp within the lamp-house. 



The metal lamp-house is shown as if transparent, as it was left in position 

 during only a part of the time while the photograph was exposed. 



Condenser and water-cell (fig. 121). 



Stage of the microscope with stage water-cell. 



Projection microscope with objectives in the revolving nose-piece, a shield 

 to stop stray light and an amplifier in the end of the large tube. 



The lamp, condenser, stage and microscope are on independent blocks and 

 can be moved freely on the optical bench. The picture of the 10 centimeter 

 rule under the door of the lamp-house gives the scale of the picture. 



R Adjustable rheostat. 



20-10 These numerals show the range of current which the rheostat per- 

 mits. The arrow indicates the way to turn the knob to increase the current 

 (see fig. 281, Ch. XIII). 



On the legs at the left is a shelf for the rheostat. 



The adjustable drawing shelf has an arrangement for moving up and down 

 on metal wavs which can be attached to any table, whatever the form of the 



