Electrical Vibrations associated with Simple Circuits. 647 
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 wi ire-length the position of the nodes may be 
known, and the distance between the condenser- plates found 
which makes the condenser circuit in tune with the wire 
system. The characteristics of the waves along the wires are 
determined by the use of the magnetic detector invented by 
Rutherford, and described by him in the Phil. Trans. clxxxix. 
(1897) p. 8. The method is the same as that given by the 
author and Vonwiller in a paper on “ Some Experiments on 
Electric 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 rect- 
angle, 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 one centimetre 
trom it. In some 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 
instances. 
In the case of straight wir es, two smail insulating tubes are 
placed symmetrically on the wire usually about 200 cms. apart. 
Each tube is encircled by a single loop of wire, the loops 
being attached by fine wires to mercury cups in a piece of 
hard rubber placed a little behind the middle of the straight 
wire, so that the ends of the solenoid of the detector may “be 
joined to them. Readings with the detector are now taken 
on discharging the condenser, for various lengths of the 
parallel wires. At each adjustment of the length, the position 
of the bridge on the wires, and the distance between the 
condenser-plates, are altered by reference to the curves ob- 
tained in the preliminary investigation, so that the condenser 
circuit is always kept in tune with the parallel wire system. 
When the amplitude of the vibration in the straight wire is 
a maximum under these circumstances, as determined by 
observations with the detector, the wave-length of the 
vibration connected with the str aight wire is considered to be 
the same as that associated with the rectangle formed by the 
parallel wires and the two bridges. Experiments with the 
other circuits have been made in a similar manner. A com- 
plete set of results was obtained by this method. 
A second plan has been to set the condenser circuit and the 
