74 



ALTERNATING CURRENTS 



Figure 71 shows the general arrangement of a laboratory type 

 of oscillograph. 



The light from the arc lamp strikes the two total-reflecting 

 prisms by means of which the beam is turned at right angles and 



PLAN 



I 



gigi 



Vibrators Cylindrical Rotating Viewing Fll 



Lens. Mirror ^Screen Drum 



-===ffl 



ELEVATION 



Shutter 



FIG. 71. Typical oscillograph. 



directed upon the vibrator mirrors at V. These mirrors reflect the 

 light back through the cylindrical lens, which concentrates the 

 beam. A plane mirror M reflects the light down to a rotating 

 mirror which in turn reflects it, drawn out as a wave, on the 



Non-inductive 

 Resistance 



Load 



Fia. 72. Method of connecting oscillograph vibrators in circuit. 



viewing screen. It is often desired to obtain a photographic 

 record of the phenomena which occur. For this purpose a sensi- 

 tive photographic film is wound on the film drum, which is 



