MECHANICAL ENERGIES OF THE SOLAR SYSTEM. 69 
perienced such an augmentation ; for according to the form of the gravitation theory 
which I have proposed, the added matter is drawn from a space where it acts on 
the planets with very nearly the same forces as when incorporated in the Sun. 
This form of the gravitation theory then, which may be proved to require a 
greater mass of meteoric matter to produce the solar heat than would be required 
on any other assumption that could be made regarding the previous positions 
and motions of the meteors, requires not more than it is perfectly possible does 
fallin to the Sun. Hence I think we may regard the adequacy of the meteoric 
theory to be fully established. 
Let us now consider how much chemical action would be required to produce 
the same effects, with a view both to test the adequacy of the theory that the 
Sun is merely a burning mass without a supply of either fuel or dynamical energy 
from without, and to ascertain the extent to which, in the third theory, the com- 
bustion of meteors may contribute, along with their dynamical energies, to the 
supply of solar heat. Taking the former estimate, 2781 thermal units centigrade, 
or 3,869,000 foot-lbs. as the rate per second of emission of energy from a square 
foot of the Sun’s surface, equivalent to 7000 horse power, we find that more than 
‘42 of a lb. of coal per second, or 1500 lbs. per hour would be required to produce 
heat at the same rate. Now if all the fires of the whole Baltic fleet were heaped 
up and kept in full combustion, over one or two square yards of surface, and if 
the surface of a globe all round had every square yard so occupied, where could 
a sufficient supply of air come from to sustain the combustion? yet such is the 
condition we must suppose the Sun to be in, according to the hypothesis now 
under consideration, at least if one of the combining elements be oxygen or any 
other gas drawn from the surrounding atmosphere. If the products of combus- 
tion were gaseous, they would in rising check the necessary supply of fresh air ; 
or if they be solid or liquid (as they might be wholly or partly if the fuel be 
metallic) they would interfere with the supply of the elements from below. In 
either or in both ways the fire would be choked, and I think it may be safely 
affirmed that no such fire could keep alight for more than a few minutes, by any 
conceivable adaptation of air and fuel. If then the Sun be a burning mass, it 
must be more analogous to burning gunpowder than to a fire burning in air; and 
it is quite conceivable that a solid mass, containing within itself all the elements 
required for combustion, provided the products of combustion are permanently 
gaseous,* could burn off at its surface all round, and actually emit heat as co- 
piously as the Sun. Thus an enormous globe of gun-cotton might, if at first cold, 
and once set on fire round its surface, get to a permanent rate of burning, in 
which any internal part would become heated by conduction, sufficiently to 
ignite, only when nearly approached by the diminishing surface. It is highly 
probable indeed that such a body might for a time be as large as the Sun, and 
give out luminous heat as copiously, to be freely radiated into space, without suf- 
* On this account gunpowder would not do. 
