WAVE-LENGTH ON STRAIGHT CONDUCTOR. 253 



The WAVE-LENGTH op the ELECTRICAL VIBRA- 

 TION ASSOCIATED with a THIN STRAIGHT 

 TERMINATED CONDUCTOR. 



By J. A. Pollock, d.Sc, 



Professor of Physics in the University of Sydney. 



[Read before the Royal Society of N. S. Wales, October 6, 1915.~\ 



To a first approximation, Abraham 1 and other writers 

 conclude from theoretical considerations that the wave- 

 length of the disturbance in free ether due to the gravest 

 electrical vibration on a thin straight terminated con- 

 ductor is equal to twice the length of the rod. This result 

 is very definitely supported by Lord Rayleigh 2 in opposition 

 to the calculation of Macdonald 3 which makes the wave- 

 length 2*53 times the length of the conductor. 



Some years ago I published an account 4 of an experi- 

 mental comparison, by a resonance method, of the periods 

 of the electrical vibrations associated with simple circuits. 

 In discussing the results, I assumed that the wave-length 

 of the oscillation connected with a narrow rectangular 

 circuit was equal to the perimeter of the rectangle, and 

 was led to think that the measurements supported 

 Macdonald's theoretical deduction as to the wave-length 

 of the vibration on a straight rod. The assumption, which 

 affects the discussion only, is, however, quite unjustifiable, 

 as the wave-length depends on the ratio of length to breadth 

 as well as on the perimeter of the circuit. Contrary to the 

 opinion I then expressed, the experimental results cannot 

 be taken as supporting Macdonald's theory. 



1 Abraham, Ann. der Physik, 66, p. 435, 1898. 



2 Kayleigh, Phil. Mag., 8, p. 105, 1904; Phil. Mag., 25, p. 1, 1913. 



3 Macdonald, Electric Waves, p. Ill, 1902. 



4 Pollock, Jour, and Proc. Koy. Soc. N.S. Wales, 37, p. 198, 1903; Phil. 



