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LXXI. A Comparison of the Periods of the Electrical Vibrations 
associated with Simple Circuits. By J. A. Pottock, Pro- 
Jessor of Physics in the University of Sydney. With an Ap- 
pendix by J.C. CLose, Deas-Thomson Scholar in Physics*. 
Introductory. 
© idee object of the present research has been to compare 
the periods of the electrical vibrations connected with 
narrow rectangular closed circuits with those of the oscil- 
lations associated with straight wires and with open and 
closed rings. 
The essential features of the experimental method adopted 
are as follows :—A condenser is discharged in the neighbour- 
hood of a narrow rectangular closed circuit ; oscillatory 
currents are thus set up in the rectangle, which in turn 
induce others in a third circuit of required shape. Obser- 
vations of the amplitudes of the disturbances in the circuits 
are made with Rutherford’s magnetic detectors, while the 
dimensions of the circuits are adjusted, step by step, until 
finally all three are in tune. The length of a circuit of any 
shape can thus be found which has the same period of 
electrical vibration as that of a given narrow rectangular 
closed circuit. 
When the experiments were commenced, it was generally 
considered, on theoretical grounds, that the wave length of 
the free oscillation connected with open resonators was equal 
to twice the length of the circuit}; and certain experimental 
evidence had lately been published? which apparently 
accorded with such a view. The well-known experiments of 
Sarasin and De la Rive and others, however, make the wave- 
length greater than twice the length of the resonator. It 
seemed essential therefore to strengthen, if possible, the 
experimental position, and w ith this object i in view the present 
experiments were undertaken. Since their practical com- 
pletion, theoretical support has been withdrawn from the 
results first mentioned, by the publication of Macdonald’s 
Adams Prize Essay on Electric Waves (Cambridge, 1902), 
which has wholly changed the theoretical aspect. 
Macdonald’s calculations so closely agree with the bulk of 
* Communicated by the Author. Read before the Royal Society of 
New South Wales. 
+ Kirchhoff, Pogg. Ann. vol. cxXl., 1864. Thomson, ‘Recent Re- 
spas ’ p. 340 ( 1893). Poincaré, ‘Les Oscillations Electriques,’ p. 273 
(G. Carré, Paris, 1894). 
t Turpain, Journ. de Phys. vol. x. p. 425 (1901); Slaby, Electrotech. 
Zeit. No. 9, p. 165 (1902). 
