1885.] 
127 
The Heat of the Sun. 
theory have been proposed, but they all fail to afford an 
adequate cause. Thus the suggestion has been made that 
the oxygen needed for combustion may be supplied from the 
material of the Sun itself, just as gunpowder is supplied 
with oxygen from the nitre it contains. But even supposing 
him to consist of gun-cotton, the substance which is better 
supplied with oxygen than any other, it is easily calculated 
that he would be burnt out, and 
. “ wander darkling in th’ eternal space, 
Rayless and pathless,” 
in less than eight thousand years. 
These various suggestions— Tor we cannot call them 
theories— we will not stop to consider. Ingenious and yet 
simple, as many of them are, they one and all fail to rise to 
the magnitudes with which they have to deal. We pass on 
to the consideration of the next, and certainly one held by 
many physicists. 
The Meteoric Theory. 
Born in the little town of Heilbronn, Wtirtemberg, the 
illustrious originator of this theory would have lived and 
died a respected German physician had he not possessed a 
strong mental bias in favour of physical speculations. In 
such a case the strong influence which his writings have 
made upon the thought of the present day would have been 
wanting, and the world would have been ignorant of the 
hame of Robert Juiius Mayer. But here we must guard 
ourselves against falling into the opposite extreme, and 
giving all the credit to one. I have called Mayer the 
originator of the theory, and so in truth he was, having pub- 
lished his “ Essay on Celestial Dynamics” in 1848. But, 
as is generally the case, other minds were at the same time 
actively engaged upon a similar subject. It was not, how- 
ever, until the Hull Meeting of the British Association, in 
1853, that Waterton sketched the same theory, being at the 
time quite ignorant of Mayer’s previous writings. Water- 
ton’s paper attracted the attention of the celebrated mathe- 
matician and physicist, Sir William Thompson, and in a 
beautiful memoir — published in the “ Transactions of the 
Royal Society of Edinburgh ” for 1854 — the whole theory is 
exhaustively worked out and developed. With the help of 
these writings we will now endeavour to give, as briefly as 
possible, an outline of this interesting theory. 
It is necessary, however, to a proper appreciation of the 
