420 Scientific Proceedings, Royal Dublin Society. 
manner as that along the tube. This result proves, at least, that 
along with the luminous discharge, there exist air disturbances, 
such as, I suppose, to be the cause of the strata (v1.). 
Taking all these facts in connexion with those already stated 
in my former paper, I venture to put forth the following line of 
argument :—Electric sparks have been shown to produce certain 
mechanical effects which, in appearance, present a remarkable 
similarity to the stratified discharge. These effects are shown to 
be due to the air disturbances caused by the electric sparks, which 
are of the same nature as the “alternating” currents mentioned 
by Lord Rayleigh. These latter effects have also been shown to 
be due to modifications in the body of the gas itself. We have 
further seen that they are present in the case of the stratified 
discharge itself. ‘hese modifications consist of node-like collec- 
tions of gaseous matter, at regular intervals, throughout the 
length of the tube. These collections of gas particles, illuminated 
by the discharge which is actually passing between them, would 
in the present theory, be a series of strata. As far as the general 
theory goes, the strata might be either true nodes or the “ rib- 
like” lines. The latter would appear to be the more easily 
produced. 
This theory would explain many difficulties which other more 
elaborate ones fail to explain; such, for example, as the general 
movement of the strata, often mentioned by those who have 
written on this subject. 
There is one point which might present a difficulty. If the 
strata are, as I suggest, a mechanical production, it is, at first 
sight, difficult to understand how they could be illuminated by 
the spark which causes them. I think this objection can be met 
by considering that the gas, at this instant, is in a state of electri- 
fication, and that this, of itself, would be a reason why the 
disturbance would be propagated with great velocity. Again, 
the origin of the disturbance is not confined to any one point in 
the tube, but seems to take place throughout its whole length, in 
which case the formation of the “ gas-strata”” would be practically 
simultaneous with the discharge. Again, the tubes remain illumi- 
nated an appreciable time after the discharge has passed. 
I think I have given ample evidence to show the existence of 
the gas disturbances demanded in this theory. It does not, there- 
