ON ELECTRICAL DISCHARGES THROUGH RAREFIED GASES. 
181 
confirmed by experiment. It is a matter of common occurrence in physics, that where 
a cause having one period acts upon a subject having a different period, the result is, 
on the average, the same as though the former remained constant at its mean value. 
Applying such considerations to the present case, we see that if the tinfoil be joined 
to a conductor whose electric state periodically changes, but whose period is not the 
same as that of the discharge in the tube, we may expect the effect to be the same as 
though it remained constant at its mean value ; that is to say, it will be the same as 
though the tinfoil were connected with the earth (supposing the conductor to be of 
sufficient capacity), since it is a matter of indifference at what potential the relieving 
conductor actually stands. Thus to whatever conductor of sufficient capacity the 
tinfoil be connected, the effect will be the same as though it were connected to earth, 
unless tire conductor have an electrical period identical with that of the discharge in 
the tube. The effect produced by joining the tinfoil to earth therefore naturally 
becomes our standard effect, with which all others may be compared. We shall in 
future call this effect the to-earth or relief-effect. 
We have said that experiment fully confirms the theoretical result that any 
conductor of sufficient capacity not having the same electrical period as the discharge 
in the tube will give the to-earth or relief-effect. And this is so. If the tinfoil be 
connected with either terminal of the Holtz machine when the current is obtained 
therefrom,* or to an independently working coil or to a wire carrying a current with 
an independent air-spark, the relief-effect will be produced exactly as though the 
tinfoil had been connected with earth. It must, of course, be understood that if the 
changes of tension in the conductor be sufficiently violent, they will of themselves 
produce inductive discharges in the tube, just as they would in the case of a tube with 
no discharge through it, and the total effect will be the sum of the relief-effect and 
these inductive discharges. But allowing for such independent effects of the variations 
in the electric state of the conductor, we have not found any exception to the rule 
enunciated above, viz., that any conductor of sufficient capacity whose electric state 
does not suffer variations of like period with the interrupted discharge in the tube will, 
when connected with the tinfoil on the tube, produce the relief-effect, that is say, the 
same effect as though the tinfoil had been connected with the earth. 
* There is sometimes, however, a slight heightening of the relief-effect when the tinfoil is joined to the 
terminal of the Holtz machine nearest to the air-spark. This is due, no doubt, to a slight periodic variation 
of tension there, caused by, and synchronous with, the pulsations of the air-spark, and its period is, there¬ 
fore, the same as that of the discharge in the tube, so that it presents no exception to the general rule 
enunciated above, 
