Electrical Vibrations in terminated Rods. 427 



(a) The variation is greatest in the thin strips, is very small 

 with thick strips, and is entirely absent in phosphor- 

 bronze wire. 



(b) It is not present owing to any variation of amplitude 

 or of damping, and disappears partially though very 

 slowly when under tension. 



2. The effect was found to be practically removed when 

 the strip was annealed, and was partially removed when it 

 was overstrained by bending it. 



3. The explanation given is that the effect is due to over- 

 strains given to the strips during the process of manufacture. 



In conclusion it is with great pleasure I express my thanks 

 to Professor Wilberforce, who suggested the investigation to 

 me and who first noticed this anomalous effect. 



George Holt Physics Laboratory, 

 University of Liverpool. 

 Dec. 7, 1912. 



XLIII. The Electrical Vibrations associated ivith thin termi- 

 nated Conducting Rods. By Professor H. M. Macdonald, 

 F.R.S* 



IN" a paper, " The correction to the length of terminated 

 rods in Electrical Problems " f Lord Rayleigh con- 

 cludes, from comparison with the corresponding electrostatic 

 problem, that the difference between the half -wave length of 

 the gravest vibration and the length of the rod tends to zero 

 when the radius of the rod tends to zero. The result is also 

 involved that the radiation from the rod tends to zero as the 

 radius does. The rod is assumed to be perfectly conducting 

 and the medium surrounding it to be such that electrical 

 discharge does not take place from the end of the rod. 



The question at issue is whether these assumptions repre- 

 sent the actual circumstances when the medium surrounding 

 the rod is such that electrical discharge, and therefore 

 radiation, can take place from the free end, as, for example, 

 in the case of Marconi's antennae J. The distribution of 

 electric force in the neighbourhood of a terminated rod or 

 wire in air, on which there are electrical oscillations, appears 

 to have been first investigated by Sarasin and Birkeland §, 

 and they conclude that there is direct radiation from the free 



* Communicated by the Author. 

 + Phil. Mag. toI. xxv. p. 1 (1913). 

 X Cf. Phil. Mag. vol. viii. p. 27(5 (1904). 



§ Comptes Rendus, vol. cxvii. p. 618 (1893) : Phil. Mag. vol. xxxviL 

 p. 241 (1894). 



