12 
MR. E. RUTHERFORD ON A MAG-NETTC DETECTOR OF 
wire. By using a sensitive detector, with a few turns round it, the variation of the 
current along the wire could readily be determined. 
If short lengtiis of wire were fixed to any portion of a Leyden jar circuit, on the 
23assage of a discharge, there was always evidence of a rapid oscillation set up in the 
wire. Each of the short circuits had a tendency to vibrate in its own naturcil period, 
but the results were complicated by the oscillations of the main circuit. 
Damping of Oscillations. 
The use of magnetized needles offers a simjffe and ready means of determining the 
damping of oscillations in a discharge circuit. 
Let L be self-inductance of discharge circuit for raj-iid currents. 
,, C = ca^Dacity of condenser. 
,, B = resistance of leads and airbreak to the discharge. 
,, Vq = 2 ^otential to which condenser is charged. 
The current y at any instant is given by 
y = 
T'V 
—F «-E/2L . t 
(LC)i 
sin 
t 
W)‘ 
The exponential term only includes the case of frictional dissipation of energy, and 
does not take into account radiation into SjDace. In the experiments at j^resent con¬ 
sidered, where the condenser is of the ty^je of a Leyden jar, there can be but very 
small amount of dissipation of energy due to radiation. 
Assuming B to be constant, the amplitude of the current decays in geometrical 
progression. 
Consider two similar small oppositely wound solenoids A and B effaced in series in 
the discharge circuit. Two magnetized needles are placed in A and B, the north 
poles facing in the same direction. After the passage of a discharge, it will be found 
that the reduction of magnetic moment is not the same in the two needles. 
Let ... be the half-oscillations of the discharge in one direction. 
,, ... be the half-oscillations in the opposite direction. 
Suppose that the half-oscillation ntj tends to magnetize the needle in the solenoid 
A still further. Since the needle is saturated no effect is jjroduced, demagnetizes 
the surface skin, tends to remove the effect of and so on. In the solenoid B 
demagnetizes the needle, (3^ tends to remagnetize it in its original direction, and so 
on. Since the maximum value of the current of ccy is greater than the maximum 
value of the needle in B will be more demagnetized than in A. 
If, however, we increase the number of turns joer centimetre on the solenoid A, 
until the effects on the two needles are exactly the same, then assuming that the 
value of the current decreases in geometrical progression, the maximum value oi the 
