1904 - 5 .] On Prof. Seeligers Theory of Temporary Stars. 533 
This figure exceeds the average velocity of the outrushing gases in 
solar eruptions, but it may nevertheless be assumed to he at least 
of the order of these velocities. If, therefore, we grant the 
reality of the motions in the case of the sun, we should find no 
difficulty in accepting the explanation of the absorption-hands in 
new stars which I have proposed in this paper. I fully admit 
that a physical explanation of such exorbitant velocities in 
expanding gases has still to be framed, and that our present 
thermodynamical views, by accepting Boyle’s law, offer no clue 
whatever. But these views, it must be remembered, are based 
on conceptions of molecular matter which we now admit to be 
imperfect. The new physics of the molecule and atom is quite 
different from that which led formerly to the kinetic explanation 
of Boyle’s law. We are no longer permitted to conceive of the 
motions of gaseous molecules at solar temperatures as being 
exclusively governed by the frequency and intensity of their 
mutual impacts, and uninfluenced by any other forces acting 
between them. A number of facts point to the conclusion that 
gases emitting line-spectra are ionised. If this view is accepted, 
we have to take into consideration the electric agencies which are 
brought into play in cases of moving electric charges, and which, 
as Professor J. J. Thomson and others have shown, influence 
profoundly our conceptions of mechanical mass and energy. The 
kinetic theory of an ionised gas is therefore different from that of 
an electrically neutral gas, because in the former internal forces, 
viz. electric agencies, are operating which are not present in the 
latter. But the existence of these electric forces demands the 
introduction of an internal virial in Clausius’ fundamental equa- 
tion, which means, in other words, that Bojde’s law is inapplicable, 
since the definition of a so-called £ perfect ’ gas excludes the 
presence of an internal virial. Now, our difficulty in under- 
standing the greatness of motions in solar eruptions arises mainly 
from the fact that we have hitherto considered the gases on the 
sun as being in this ‘ perfect ’ state, and therefore have accepted 
Boyle’s law as the basis from which we formed our opinions of the 
greatest possible speeds in expanding gases at solar temperatures. 
We have reasoned in the following way : The velocity with which 
a certain disturbance of equilibrium within the gas can be propa- 
