534 Proceedings of Royal Society of Edinburgh. [sess. 
gated by internal mechanical agencies can under no circumstances 
exceed that with which sound would travel through the gas. Now, 
we have a fairly warranted estimate of the surface temperature of 
the sun, and with this temperature we can compute the speed of 
sound in the solar chromosphere. But we find that the computed 
velocity falls considerably short of that usually noticed in solar 
prominences. Hence we argue that the phenomenon of solar 
eruptions cannot be explained on the basis of thermodynamical 
reasoning. The argumentation seems strong enough, only we must 
not forget that our computation of the velocity of sound is essen- 
tially founded on Boyle’s law. If, for instance, we assumed 
that between the molecules of the solar gases powerful repulsive 
forces were acting, the computed speed of sound would become 
considerably greater, and hence our conclusion as to the maximum 
speed of propagation would also differ from that we hold at present. 
We are, I think, clearly placed before the alternative : either 
Boyle’s law is correct, then it is difficult to see how solar eruptions 
can be real displacements of matter ; or Boyle’s law does not 
express the true kinetic conditions existing in solar gases, then the 
high velocities in solar eruptions become conceivable if we assume 
powerful repulsive forces acting between the molecules. As I 
mentioned before, there are reasons which seem to favour the 
second alternative. If, for instance, we accept the modern view 
that radiation is due to motions of the electrons within the atom 
or molecule, are we not bound to look upon the molecules of an 
incandescent gas as moving electric currents ? And suppose, under 
this condition, two molecules to approach each other, will not the 
induced electric force tend to drive them apart, i.e. act as a 
repulsive force 1 ? We are quite certain that this will happen in 
the case of ordinary currents and conductors, such as we are able 
to produce in laboratories : why not also in currents of molecular 
dimensions ? What difference is there between a current produced 
by electrons moving along a conducting wire, and one caused by 
electrons moving round the nucleus of the atom or molecule ? I 
think questions of this kind may at least shake the hitherto 
implicit confidence in the so-called * perfect ’ state of incandescent 
gases, and may also make us aware that the kinetic theory of 
matter endowed with distinct inherent electric properties must 
