178 
MESSRS. W. SPOTTISWOODE AND J. FLETCHER MOULTOH 
afforded by conductors for an explanation of their effect on the sensitive discharge. 
This conclusion is supported by the fact previously stated that a small piece of tinfoil 
placed upon the tube produces no effect so long as it is insulated. Such a piece of 
tinfoil would give but little scope for redistribution of electricity—at all events, in 
such a way as to affect the space around it. But if it be' connected metallically with 
•a distant conducting body, so that positive or negative electricity can be driven from 
it to a sensible distance from the tube, the case is different ; and if this be done it is 
at once found to affect the sensitive discharge. 
If, then, the effect on the sensitive discharge is caused by the facility for a redis¬ 
tribution of electricity within the portion of the electric field occupied by the conductor, 
it fohows that there must be a varying electric action upon it from the discharge in the 
tube. And that such is the case may be shown by connecting a ring of tinfoil placed 
round the glass with the earth, and interposing a telephone in the circuit between the 
tinfoil and the earth. So soon as the current becomes interrupted by an air-spark, a 
sound is heard in the telephone corresponding with the sound of the air-spark causing 
the intermittence. This shows conclusively that at each pulsation there is an electrical 
redistribution within the system composed of the earth, the wire, and the tinfoil. And 
as this continues indefinitely, without producing any charge upon the tinfoil, it is clear 
that there must, during the complete period of each pulsation, be a flow of one kind of 
electricity from the tinfoil, followed by its return or a similar flow of the opposite kind 
of electricity from the tinfoil. „ 
Now, since this periodic redistribution is effected by the pulsations of electricity 
within the tube, it follows that we may regard the conductor as affording a kind of 
relief to the tension in the electric field round the portion of the tube with which it is 
in contact. And that such is the nature of its action can be shown by numerous 
experiments, such as the following : If, instead of connecting the tinfoil to earth, a 
wire leading to earth be placed almost in contact with it, sparks will be seen to pass, 
showing the state of electric tension to which the tinfoil is from time to time subjected. 
And further, if the effect upon the sensitive discharge be examined closely, it will be 
found to be stronger in proportion as the circumstances in which the tinfoil is placed 
are more favourable for giving more complete relief. So long as the wire does not 
touch the tinfoil, or permit sparks to pass from or to it, the tinfoil is unable to affect the 
sensitive discharge. But if the wire be near enough for sparks to pass, the sensitive 
discharge will be affected, but to a decidedly less extent than would be the case were 
the wire in actual contact with it. In the latter case the relief which it could afford 
would be perfect; in the former it would be imperfect, since the sparks would not be 
able perfectly to equalize the potentials of the tinfoil and the wire. Again, the effect 
of the tinfoil when in electrical connexion with the conducting body will be found to 
vary in proportion to the capability of the system to relieve the tension of the tinfoil. 
If the conducting body be large or distant, the effect will be nearly the same as though 
