176 
MESSRS. W. SPOTTISWOOJDE AND J. FLETCHER MOULTON 
truth, there is no impossibility in producing by a single flash a discharge having 
the characteristics of sensibility. If a charged Leyden jar'" (“ On Stratified Discharges, 
IV.,” Proceedings of the Royal Society, March 22, 1877) be employed with a suitable 
tube, the instantaneous discharge that passes through the tube on the jar being 
connected with it will show all the symptoms of sensitiveness during its passage 
through the tube. 
This direct evidence of the connexion between intermittence of discharge and the 
sensitive state will, we believe, derive further support from the accordance of the 
various phenomena with the theory of the sensitive state which will be developed in 
the course of this paper, and which rests upon the hypothesis that the sensitive state 
is due to such an intermittence—a hypothesis which the authors of this paper venture 
to hope is sufficiently demonstrated by the experimental facts already stated. 
In conclusion, the authors of this paper desire it to be understood that, in claiming 
intermittence as an essential of the sensitive discharge, they do not intend to exclude 
all ideas of intermittence from the non-sensitive discharge. The experiments of Sir 
W. Grove,! Mr. De La Rue, and others, have shown almost to demonstration that 
there is intermittence in the most stable and non-sensitive discharges. But such 
intermittence must be of an order almost incomparably higher than that of which we 
are speaking. Though sensitiveness has been found to co-exist with intermittence at 
the highest speeds attainable by the mechanical or chemical means above referred to, 
and even in many cases to increase with the rapidity of intermittence, it is by no 
means necessary that it should continue to do so when this rapidity is increased, say, 
many hundred or thousand fold. Indeed, with the rapidity given by a short and rapid 
air-spark, the sensitiveness is not so marked in its features as with a longer and less 
rapid air-spark. Nor, as will be seen, does our view require that very great rapidity 
of intermittence should necessarily jDroduce very great sensitiveness. On the contrary, 
so far from its being an advantage that the discharge should be divided into a very 
large number of small discrete discharges, it would seem that the most favourable 
condition for the production of sensitiveness is that the individual discharges should 
be as large (and therefore as few in number) as is compatible with an absence of the 
prolonged or fluctuating phases observed in the ordinary coil discharge.} And there¬ 
fore, in order to avoid any misconception, the terms interrupted and uninterrupted 
will be used to describe the condition of the currents causing the sensitive and non¬ 
sensitive state respectively, instead of the terms intermittent and continuous, which 
might otherwise have been adopted. 
* This experiment will be found more fully described on p. 208, and properly belongs to a later portion 
of the investigation, and is referred to here only in passing, 
t Phil. Mag., 1858, July-December, p. 18. 
+ It will be found that this conclusion, which was arrived at from observation, is a necessary con¬ 
sequence of the theory of sensitiveness which the authors of this paper desire to put forward. 
