MECHANICAL ENERGIES OF THE SOLAR SYSTEM. 65 
velocities which they have acquired by his attraction. This is a form of what may 
be called the Gravitation Theory of Solar Heat, which. is itself included in the 
general meteoric theory. 
The objects of the present communication are to consider the relative capa- 
bilities of the second and third hypothesis to account for the phenomena; to ex- 
amine the relation of the gravitation theory to the meteoric theory in general ; and 
to determine what form of the gravitation theory is required to explain solar 
heat consistently with other astronomical phenomena. 
In the first place, it may be remarked, that in all probability there must always 
be meteors falling into the Sun, since the fact of meteors coming to the earth* 
proves the existence of such bodies moving about in space ; and even if the mo- 
tions of these bodies are at any instant such as to correspond to elliptical or 
circular orbits round the Sun, the effects of the resisting medium would gra- 
dually bring them in to strike his surface. Also, it is easy to prove dynamically 
that meteors falling in to the Sun, whatever may have been their previous state 
of motion, must enter his atmosphere, or strike his surface, with, on the whole, 
immensely greater relative velocities than those with which meteors falling to the 
earth enter the earth’s atmosphere, or strike the earth’s surface. Now, JouLE has 
shewn what enormous quantities of heat must be generated from this relative 
motion in the case of meteors coming to the earth; and by his explanation} of 
“ falling stars,” has made it all but certain that, in a vast majority of cases, this 
generation of heat is so intense as to raise the body in temperature gradually 
up to an intense white heat, and cause it ultimately to burst into sparks in the 
air (and burn if it be of metallic iron) before it reaches the surface. Such effects 
must be experienced to an enormously greater degree before reaching his surface, 
by meteors falling to the Sun, if, as is highly probable, he has a dense atmosphere ; 
or they would take place yet more intensely on striking his solid or liquid surface, 
were they to reach it still possessing great velocities. Hence, it is certain that 
some heat and light radiating from the Sun is due to meteors. It is excessively 
probable that there is much more of this from any part of the Sun’s surface than 
from an equal area of the earth’s, because of the enormously greater action that 
an equal amount of meteoric matter would produce in entering the Sun, and be- 
cause the Sun, by his greater attraction, must draw in meteoric matter much more 
copiously with reference to equal areas of surface. We would have no right then, 
as was done till Mr Wartersron brought forward his theory, to neglect meteoric 
action in speculating on solar heat, unless we could prove, which we certainly 
* To make the argument perfectly conclusive, it would have to be assumed that meteors not 
only are, but have been, always falling to the earth for some immense period of time, The conclu- 
sion, however, appears sufficiently probable with the facts we know. 
{ See Philosophical Magazine, May 1848, for reference to a lecture in Manchester, on the 28th 
April 1847, in which Mr Joutz said, that “ the velocity of a meteoric stone is checked by the atmo- 
sphere and its vis viva converted into heat, which at last becomes so intense, as to melt the body and 
_ dissipate it in fragments too small probably to be noticed in their fall to the ground, in most cases.” 
