i88 5 .] 
The Heat of the Sun. 
125 
differing only from our terrestrial fires in magnitude and in 
the intensity of its combustion. Now as the substance 
which we use most extensively, and which gives us more 
heat than any other common substance, is carbon, conse- 
quently it has been suggested that the Sun consists of a 
mass of carbon in an adtive state of combustion. This, 
then, is the first crude idea which was held respecting the 
constitution of the Sun. Before we allow ourselves to 
wonder at the authors for proposing so unsatisfactory an 
explanation, we must bear in mind the “ nature of the en- 
vironment,” if I may so call it, in which they were placed. 
In the first place the distance of the Sun was not thought so 
immense as it is now proved to be ; secondly, the age of the 
Earth was not considered so great as at present, — conse- 
quently a less powerful cause had to be found; and thirdly, 
those wonderful discoveries of the spectroscope which have 
revealed to us the physical construction of the Sun had not 
been made. 
Now in order that combustion, as we term it, should go 
on, there must be some substance with which the combus- 
tible body can combine. Here on our Earth this body is 
known to be oxygen, and it is supposed that the same body 
exists in the Sun, and by its combination with the carbon 
produces the heat which we find given out. Again, we know 
that 1 lb. of pure carbon, in burning so as to produce the 
greatest amount of heat, combines with 2§ lbs. of oxygen. 
Also one cubic mile of pure oxygen will weigh about 
13,189,120,000 lbs. Now on every square yard of the Sun’s 
surface there is given out as much heat as would be pro- 
duced by the burning of 6 tons of carbon per hour : 6 tons 
of carbon will require 35,840 lbs. of oxygen, and such an 
amount of oxygen would be contained in a column 1 square 
yard base and 14,336 yards high. Thus in every hour the 
Sun uses up a column of pure oxygen 8'3 miles high, and of 
the density of the gas at the average atmospheric pressure 
here on the Earth. But the attraction of the Sun upon 
any body placed near it is, in consequence of its mass, very 
nearly thirty times as great as the attraction of the Earth 
upon the same body. We will thus reduce the height of 
this column this number of times, and thus obtain that 
every hour there is used up a shell of about 3-ioths of a 
mile thick around the Sun of pure oxygen. (This difference 
in attractive power is only mentioned to guard against mis- 
representation, and for the purpose of making the latter 
part of the argument more conclusive.) The immense heat 
of the Sun would expand gaseous bodies so much as to 
