DETERMINATION OF WAVE FORM 



637 



of the string galvanometer has been employed by some designers, 

 for in this instrument there is no mirror to be moved. 



In Fig. 401 the shell and pole pieces of an iron-clad electro- 



3-4 



3-4 



8 Tfg X 7 



I'n;. 401. Ganz oscillograph, a modified string galvanometer. 



magnet are at 1 and 2. The exciting coils are at 5. The strength 

 of hVld in the air gap is from 28,000 to 30,000 c.g.s. units. 



The moving parts or "strings" are at 6. Starting from the 

 terminal 9 the thin metal strip which serves as the " string " passes 

 down between the bridges 3 and 4, 

 along the air gap to 3' and 4', around 

 the pulley and up between the same 

 set of bridges to the terminal 10. 

 Both the descending and the ascend- 

 ing parts of the strip are thus brought 

 into the same plane. The free vibrat- 

 ing length of the strip is from 3 to 5 

 cm. The necessary tension is given 

 by the spring 7 and a period of from 

 M>ooo to %,ooo second is obtained. 

 At 8 is a third terminal which is 

 common to the two parts of the strip, 

 one of which is used for the current, the other for the potential 

 vibrator, as is indicated in Fig. 402. 



A hole is bored axially through the pole pieces so that by means 



D.C. 



FIG. 402. Arrangement of 

 circuits in Ganz oscillograph. 



