ON ELECTRICAL DISCHARGES THROUGH RAREFIED GASES. 
209 
and that the effect of the rapid repetition of the discharges is merely to give the 
appearance of permanence to effects which in reality appear and disappear during each 
separate discharge. 
'XI.— The discharge is effected under ordinary circumstances by the passage through 
the tube from the air-spark terminal of free electricity of the same name as 
the electricity at that terminal. 
The knowledge derived from our previous experiments of the difference between the 
effects of positive and negative pulses arriving at the outside of the tube, enables us to 
ascertain the nature of the electrical disturbances within the tube, for as we have seen 
there is a complete dissimilarity between the appearances produced within the tube 
by the two kinds of pulses. Now, if we take a tube containing an ordinary sensitive 
discharge in which the sensitiveness is produced by an air-spark and connect tinfoil 
placed upon it to earth, we get the same type of effect wherever we place the tinfoil. 
Thus, if the air-spark be in the positive portion of the external circuit, the effect of 
joining to earth a piece of tinfoil placed upon any part of the tube will be what we 
may term a negative effect, showing that throughout the tube the primary and main 
effect is a sudden irruption of positive electricity across the section of the tube beneath 
the tinfoil.* This is the case even though the tinfoil be placed very close to the nega¬ 
tive end of the tube. Thus throughout the whole length of the tube the charge of 
positive electricity passes without awakening a response from the other terminal, or if 
there be any response it must be a very faint one so as not in any way to make doubtful 
the very great preponderance of the original charge. If the negative be the air-spark 
terminal the same result is observed, with the exception that the charge passing 
through the tube is of negative electricity. 
It must be observed that in saying this we do not commit ourselves to the two-fluid 
theory of electricity, or to any equivalent theory. It may be that instead of a charge 
of negative electricity being thus sent through the tube the thing that is propagated 
is a state of deficiency of positive electricity. Nor do we necessarily adopt any special 
theory of the propagation. It may be that the electricity is carried on material 
particles of gas; it may be that it is passed from one particle to another without or in 
addition to the actual motion of the particles charged with it at any moment; or it 
may be propagated without the assistance of the material particles of the gas. Which 
* These remarks are strictly only applicable to cases in wbicb the discharge in the tube would, without 
the interposition of the air-spark, be non-sensitive. Those tubes which of themselves render discharges 
sensitive must be regarded as tubes, one or both terminals of which act as though there were an 
air-interval essentially connected with them, so that when using such tubes with an external air-spark 
we are often in the position of using a tube with an air-spark in both the positive and negative external 
circuits. The phenomena in such cases are of course somewhat complicated, as special effects (though 
different in character) are obtained by connecting the tinfoil to either terminal, but otherwise they 
present no theoretical difficulty, and will not be further noticed in this paper. 
MDCCCLXX1X. 2 B 
