Impulsive Motion of an Electrified Sphere. 43 



With (\ = 11*87 mfd. the frequency of the arc note was 

 578, and of the damped oscillation 678. In these cases also 

 the arc frequencies are considerably less than those of the 

 same circuits without the arc. 



With Ci = 9'55 and C 2 about -000275 mfd. one note was 

 heard, and the secondary potential reached very high values 

 during the oscillations, as was shown by copious " brushing " 

 at the plates of the secondary condenser. The curve is 

 shown in PI. I. fig. 11. The amplitude was at times 

 even greater than is there shown, and the zero-line had to be 

 brought below the tuning-fork wave in order to keep the 

 vibrating ray on the rotating mirror. The frequency is 613, 

 and the octave appears to have an amplitude several times as 

 great as that of the fundamental. The value of L^Cx is 

 4*411 x 10 -8 , of L 2 C 2 about 1*929 x 10 -8 ; the frequencies 

 calculated by (4) from the inductances and capacities are 

 approximately 723 and 1300. The high potential at the 

 plates of the secondary condenser in this case appears to be 

 due to approximate agreement in frequency between the 

 octave of the arc note and the higher natural vibration of 

 the secondary coil. Similar evidences of " resonance " of a 

 transitory kind were frequently observed with the other 

 condensers when the arc note (either the high note or the 

 low note) during its fluctuations fell rather low in pitch. 

 All the effects here described may also be conveniently 

 obtained by using a variable condenser with oil dielectric 

 as the secondary capacity. 



Bangor, September 1908. 



III. The Impulsive Motion of an Electrified Sphere. By 

 G. F. C. Searle, M.A.j F.R.S., University Lecturer in 

 Experimental Physics, Cambridge*. 



§ 1. 4 T the end of a paper on a The Impulsive Motion of 

 jTJl Electrified Systems," t published in the Philoso- 

 phical Magazine for January 1907, I have calculated the 

 energy and momentum radiated when the velocity of a 



* Communicated by the Author. 



t I regret that when I wrote this paper I was unaware that Dr. Paul 

 Hertz had obtained some of the results in his Untersuchungen iiber inistetiye 

 Beweyungen eines Electron*, Gottingen, 1904. His paper was io my 



possession at the time, but I was under the impression that it referred 

 to the force required to set a charged sphere in motion and not to the 

 problems which I was considering-. Where my work overlaps that of 

 Dr. Hertz, it gives an independent confirmation of his results, as it was 

 done without any reference to his paper. 



