76 ALTERNATING CURRENTS 



ripples in the curve). In order to prevent distortion of the luminous 

 speck formed on the screen, the glass tube is fitted with a small lens, 

 through which the light enters and leaves the tube. The tubes con- 



4-viBRATiKt BAND 

 oa STR.IP 



r 



METHOD OF FIXING 

 STRIP 



FIG. 58. Details of Blondel Oscillograph. 



taining the bands slip into the spaces between the laminated pole- 

 pieces and central core of the controlling magnet shown in Fig. 57. 

 Besides the oscillograph just described, Blondel devised another 



