I 
1877.] Probable Origin and Age of the Sun . 319 
such, condensation — under the influence of the mutual at- 
traction of its particles — would commence. We must 
therefore assume either that the mass was created at the 
moment condensation began, or that, prior to this moment, 
it existed under some other form. There are few, I think, 
who would be willing to adopt the former alternative. If 
we adopt the latter we must then ask the question, In what 
condition did this mass exist prior to the commencement of 
condensation ? The answer to this question would naturally 
be that it existed in a condition of excessive temperature, 
the repulsive force of heat preventing the particles approach- 
ing one another. In short, the excessive temperature was 
the very cause of the nebulous condition. 
But if the mass was originally in a heated condition, then 
in condensing it would have to part not only with the heat 
of condensation, but also with the heat which it originally 
possessed. 
It is therefore evident that if we admit that the nebulous 
mass was in a state of incandescence prior to condensation, 
it will really be difficult to fix any limit either to the age 
of the sun or to the amount of heat which it may have 
originally possessed. The 20 million years’ heat obtained 
by condensation may in such a case be but a small fraction 
of the total quantity possessed by the mass. 
The question now arises — By what means could the 
nebulous mass have become incandescent ? From what 
source could the heat have been obtained ? The dynamical 
theory of heat affords, as was shown several years ago,* 
an easy answer to this question. The answer is that the 
energy in the form of heat possessed by the mass may have been 
derived from Motion in Space. Two bodies, each one-half 
the mass of the sun, moving diredtly towards each other 
with a velocity of 476 miles per second, would by their con- 
cussion generate in a single moment 50 million years’ heat. 
For two bodies of that mass, moving with a velocity of 
476 miles per second, would possess 4149 x 10 38 foot-pounds 
of kinetic energy, and this converted into heat by the 
stoppage of their motion would give out an amount of heat 
which would cover the present rate of the sun’s radiation 
for a period of 50 million years. 
Why may not the sun have been composed of two such 
bodies ? And why may not the original store of heat pos- 
sessed by him have all been derived from the concussion of 
these two bodies ? Two such bodies coming into collision 
with that velocity would be dissipated into vapour and con- 
verted into a nebulous mass by such an inconceivable 
amount of heat as would thus be generated ; and when 
* Phil. Maff, for Mav. 1868, 
