﻿Oscillations on Iron in a Magnetic Field. 113 



The calculated period of the stationary waves on the oscil- 

 lation-coil is 5*7 x 10 -7 second. 



A typical set o£ operations was as follows. The iron was 

 demagnetized by reversals. An amplitude of cycle being 

 then decided upon, the iron was taken a number of times 

 through that cycle. This last operation was stopped at the 

 point settled upon for the observations, and the magnetometer 

 reading taken. A spark was passed, and the magnetometer 

 again read after 30 seconds. A complete cycle was now per- 

 formed ending at the same point as before, and another spark 

 passed, and so on. Usually, about twenty points on a cycle 

 were examined by 4 or 6 observations at each. In this paper, 

 however, the effects of the spark are recorded as if the 

 observations had been taken only on the ascending half of 

 the hysteresis curve ; the figures given being in fact the 

 means of the measured effects at points symmetrical with 

 regard to the origin on the ascending and descending 

 branches. 













Table I. 



















Current in 

 milliamperes. 



1 

 -150-100 



—75 



-50 



-40-30 



-20 



20 



30 



40 



50 



75 



100 



150 



200 



50 cycle 





... 







006 0-10 



013 0-28 



038 



045 



0-60 



055 







100 cycle ... 









0-27 







... 068 



1-08 



... 



... 



1-26 



1-30 



1-18 







150 cycle . . . 





020 



... 



0-44 





... 092 





1-32 





1-51 



1-62 



i« 



119 





200 cycle ... 



020 



036 





068 







... 



157 



... 



1-71 



1-75 



1-55 093 



0-83 





In this table the figures given can be reduced to absolute 

 measure as follows: — The numbers at the top of each column 

 and down the left column, representing the current through 

 the solenoids in milliamperes, yield when multiplied by 0*0(i96 

 the magnetic field in C.Gr.S. units applied to the iron. The 

 deflexions in the body of the table give the change in pole- 

 strength, due to the spark, by multiplying by 0*017 ; or 

 yield the volume-average change of intensity of magnetization 

 by the factor 1*27; or give change of total magnetic moment 

 of the affected specimen by the reducing factor 0*91:0. 



Fig. 2 is plotted from the above table. The curves show 

 clearly how for increasing cyclic amplitudes, within the 

 range here attempted, the effect of the same spark is increased. 

 The curves show very distinct maxima. It is evident, more- 

 over, that the magnitude of the effect at any point is closely 



Phil Mag. S. 6. Vol. 12. No. 6$. Aug. 1906, I 



