640 Prof. Pollock: Comparison of Periods of 
may be affected by the diameter of the wire of which the 
resonators are made. | 
Closed Rings—In Ann. der Physik, vi. 4, p. 741 (1901), 
Kiebitz shows how a filings-coherer may be used to determine 
the existence of electrical resonance. In one set of experi- 
ments, the coherer was placed across a gap in a circular 
resonator. ‘The oscillator was a straight wire 77 ems. long. 
It is stated, as the result of these trials, that with such a 
resonator there is the best response when its length is equal 
to the wave-length of the radiation falling on it. This is 
asserting a little too much. The only statement justified by 
the experiments, on this point, is that the resonator gives the 
best response when its length is double that of the straight- 
wire oscillator. 
Kiebitz’s resonator must be considered a completely closed 
ring, and his experiment proves the possibility of inducing 
oscillations in connexion with such a circuit. The present 
experiments give a result not differing greatly from that 
just stated. 
Turpain (Journ. de Phys. vol. x. p. 434, 1901), from experi- 
ments with the resonator inclosed in an exhausted glass tube, 
says :—“‘ If one completely closes the gap no current circulates 
in the closed circuit which the resonator presents. The 
electric density is zero at every point of the circuit at each 
instant.” In view of Kiebitz’s experiment this statement 
must be considered inaccurate. 
The result of the present experiments on closed rings may 
be stated as follows :—Taking as a standard the period of the 
electrical vibration associated with a narrow rectangular 
closed circuit, where the longer side of the rectangle is 
parallel to the direction of propagation of the waves, an 
elliptical closed circuit of very small eccentricity, with its 
major axis parallel to the same direction, may be considered 
to have the same period of electrical vibration if its perimeter 
is equal to that of the rectangle. If the eccentricity of the 
ellipse is increased, the perimeter has to be decreased to 
keep the period of vibration unaltered, until in the limit, 
when the form becomes circular, the ratio of the perimeter 
of the rectangle to the circumference of the circle becomes 
1:11 for a circle 800 cms. in circumference, the circle being 
made of copper wire 0°33 cm. in diameter, and the rectangle, 
30 cms. wide, of thin brass wire 0°04 cm, thick. If the 
form of the circuit is further altered, so that the major axis 
of the ellipse becomes at right angles to the direction of 
propagation of the waves, the perimeter has to be further 
decreased to keep the period unchanged. 
