606. x Mr. O. U. Vonwiller on the Dielectric 
the condenser plates by brass rods 3 millimetres thick and 
30 centimetres long, bent into an approximately circular 
form. Two brass plates, dd’, 8°8 centimetres in diameter, 
are held 8 millimetres from the plates of A, and attached to 
them are brass wires db, d'b’, °36 millimetre in diameter and 
30 centimetres apart except the parts dn, d’n’, each 27 centi- 
metres long, where the wires curve in. ‘Two bridges of 
copper wire aa’ and bb’ are placed across these brass wires. 
The circuit daa‘d’ is called the Primary, and abl'a’ the 
Secondary. Across the wires is placed a light wooden slider, 
the wires passing through small glass tubes attached to it; 
round each of these tubes is a single loop of wire which leads 
to the terminal of a Rutherford detector, the deflexions pro- 
duced by which on a magnetometer were used in determining 
the character of the oscillations set up in the wires. The 
details of the detector and the method of using it are similar 
to those described by Prof. Pollock and the author in their 
experiments on Electric Waves in Short Wire Systems (Phil. 
Mag. June 1902). 
With the bridge aa’ at a distance of 170 centimetres from 
nn’, the wooden slider carrying the detector being 5 centi- 
metres from nn’, the capacity of A was altered by varying 
the distance between the plates until the primary was in 
resonance with the condenser vibration, the deflexions pro- 
duced by the detector being greatest when this is the case. 
The effective length of the primary is now = , where Vis the 
wave-length of the condenser radiation. By altering the 
position of the bridge bb’ the secondary can be brought into 
resonance with the primary, this being the case when its 
effective length is A, the correct position being determined 
by keeping the slider midway between the two bridges, 7. e. 
at a loop of the wave, and altering the length of the circuit 
until a maximum deflexion is obtained. 
In these experiments a condenser OC was placed across the 
wires of the secondary at some place cc’. The effect of this 
capacity is equivalent to an addition to the length of the 
wires, the wave-length of free vibrations in the circuit abla! 
being given by A in the equation 
t 27a t Qerb = ar C 
CON ae a COU ogra tena 
as shown by Morton (Phil. Mag. May 1897). a and 6 being 
the distances from the middle points of the bridges aa’ and 
bb’ respectively to the condenser, C the capacity of the 
