igo 5 .] 



McCLELLAN— USE OF- OSCILLOGRAPH. 



167 



difficulty, the oscillograph has been devised, by which it is possible 

 to obtain the form of a single wave, or a number of successive 

 waves. 



The oscillograph is essentially a galvanometer of very short 

 period. The one used in this work as shown in Fig. i is of the 

 moving coil type, made under the Duddell patents. The field is 



Fig. 



supplied by an electromagnet, the coils of which are wound in sev- 

 eral sections, so that different voltages may be used for the exciting 

 current. The normal current nearly saturates the core, so that 

 slight changes in the value of the current do not cause appreciable 

 changes in the strength of the field. The coil consists of an in- 

 verted U with the ends rigidly fastened at the bottom by a rubber 

 block, and connections made to the binding posts. The upper 

 loop is threaded over a small pulley, to which is fastened the spring 

 by means of which the tension is applied to the strips. There are 

 two distinct loops, thus permitting the taking of two curves simul- 



