Electric Waves along Wires. 



655 



deflexion of the magnetomer-needle observed. The difference 

 between this and the standard saturation deflexion was a 

 measure of the intensity of the oscillations at ft. 



ft was necessary to allow the sparking to continue for some 

 definite time, for "the amount of demagnetization of the de- 

 tector-needle depends not only on the intensity of the oscil- 

 lations of certain period producing the variable magnetic 

 field, but also on the number of those oscillations*. ^ In these 

 experiments, the dependence of the demagnetization on the 

 period of sparking was appreciable as shown by 



fig- 



w 



Inch 



Fig. 2. 



190 



180 



170 



3 160 



150 



140 



— *■ * if- 



10 15 



Time in seconds. 



20 



was obtained by plotting magnetometer deflexions as # ordi- 

 nates, and times from the commencement of oscillation as 

 abscissae. The first second in this case produced about 89 per 

 cent, of the total demagnetization; after this the rate of 

 change rapidly fell off. The period of sparking chosen for 

 the following experiments was 15 and sometimes 20 seconds. 

 A small error in the time observation did not then appreciably 

 affect the result. 



The greatest trouble experienced throughout these experi- 

 ments was that occasioned by the irregularity of the sparking, 

 many long series of observations being entirely useless for 

 exact determinations. 



ft appeared that long periods of sparking were productive 



* See Kutlierford. 



