634 



ELECTRICAL MEASUREMENTS 



For demonstration purposes oscillographs are made which are 

 capable of projecting the curves on a screen. They are provided 

 with large mirrors and have a free period of from Jf >soo to 



FIG. 398. Oscillograph galvanometers. A, Cambridge Scientific Instru- 

 ment Co.; B, General Electric Co. 



second. Fig. 399 shows such an instrument* together with 

 the auxiliary apparatus. It is provided with two vibrators 

 * Pesigned and built by H. G. CRANE, Brookline, Mass. 



