PERIODS OF ELECTRICAL VIBRATIONS. 213 
period it is desired to compare with that of the rectangle 
formed by the parallel wires and the two bridges. In Fig. 4 
the position of various third circuits used is shown in 
dotted lines. 
A preliminary investigation has to be made to determine 
the relation between the length of the wires cc, and the 
distance between the condenser plates when the wire 
system and the condenser circuit are in tune. The pro- 
cedure is as follows:—With a given length of the wires, 
observations are taken of the waves along them due to a 
discharge of the condenser, for different distances between 
the condenser plates. That position of the condenser plates 
is sought which is connected with the strongest vibration 
in the wire system with three nodes in its whole length. 
The investigation is made for various lengths of the wires, 
and curves are then drawn so that for any wire length the 
position of the nodes may be known, and the distance 
between the condenser plates found which makes the con- 
denser circuit in tune with the wire system. The charac- 
teristics of the waves along the wires are determined by 
the use of the magnetic detector, invented and described 
by Rutherford.’ The method is the same as that given by 
the author and Vonwiller in a paper on “‘Some Hxperiments 
on Hlectric Waves in short wire systems,’’ published in the 
Phil. Mag. for June 1902. 
To determine the length of a circuit of given shape which 
has the same period of electrical vibration as that of a 
rectangle, the circuit is placed behind the bridge d, as shown 
in Fig. 4, with a portion of it at which is situated a current 
loop, parallel to the bridge at a distance of about 1 cm. 
fromit. Insome experiments the terminal bridge has been 
removed and the ends of the parallel wires attached directly 
to the third circuit. The results have been the same in both 
* Rutherford—Phil. Trans. chxxx1x., (1897) p. &. 
