650 
MESSRS. W. SPOTTISWOODE AND J. FLETCHER MOULTON 
of gas would have done (save that they remained fixed to the glass instead of hound¬ 
ing off and causing phosphorescence), we determined to see whether they could be 
made to show the sensitive effects which we had observed in phosphorescence. Ac¬ 
cordingly, a narrow slip of tinfoil was placed round the tube near its middle point, and 
connected to earth, and a discharge with a sharp positive intermittence was sent 
through the tube for a very short time. On examining the tube it was found that 
there was the usual thick coating of lamp-black over the sides of the tube, except 
where the tinfoil had been. This remained bare of lamp-black. Thus the relief- 
molecular streams from under the tinfoil had swept away the particles of lamp-black 
that would otherwise have lodged on the sides of the tube under the tinfoil.* 
We next joined the tinfoil metallically to the positive terminal so as to produce 
positive special. The result was that the deposit was thicker beneath the tinfoil than 
elsewhere, corresponding to the appearance of phosphorescence on the tinfoil in a like 
case. Negative relief gave a similar effect, while negative special kept the surface of 
the tube beneath the tinfoil clear of lamp-black. Thus, in all four cases the streams of 
lamp-black behaved in all respects as molecular streams would have done.t 
Seeing, then, that any small light particles of a conducting substance are capable, 
under the action of negative discharge, of forming streams similar to the molecular 
streams that produce phosphorescence, and governed by like laws, the question 
naturally suggests itself whether these molecular streams have any necessary electrical 
function to perform in the discharge, or whether the particles of the gas are not driven 
off, like the particles of lamp-black, just because they happen to be there and are 
capable of being so driven off. This is a most important and difficult question to 
decide. At present we have come to no definite conclusion upon it, but we cannot say 
that we are aware of anything that conclusively shows that they have any definite 
electrical function to perform in the discharge, while on the other hand there are many 
things that point to an opposite conclusion. 
In the first place, neither the telephone nor the standard-tube recognises their 
existence. A piece of tinfoil will cause no louder sound in a telephone nor produce 
any greater effect on a standard-tube with which it is connected because it is on a spot 
where there is brilliant phosphorescence. Nor do they take notice of its total or 
partial absence. It makes no difference whether or not the tinfoil is situated in an 
absolute or a virtual shadow, and therefore protected from the impact of these 
streams. 
* In order to ascertain that it was an electrical effect and not merely the effect of something being 
placed round the tube which might have the effect of deadening vibration, or producing some other 
mechanical effect, the experiment was tried with a ring of tinfoil unconnected with any relieving system, 
and also with an india-rubber band. In neither case was the coating of lamp-black affected. 
f It is necessary that the discharge should be brief in duration, for otherwise the whole surface has a 
tendency to get coated. It must be remembered that the lamp-black accumulates on the surface, so that 
it is only by so doing that the conditions resemble those under which phosphorescence is produced. 
