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various difficulties that suggest themselves at every turn 
and find a solution to them consistent with it. 
I believe these difficulties are not hard to meet. It will 
be noticed that in the question I propounded at the head of 
this paper I use the word directly or immediately. When 
I say that the earth is itself the furnace which supplies the 
phenomena of heat which we study and feel I do not mean 
that it does so entirely per se, and without any assistance 
from without. I predicate all through that such heat as 
the earth possesses is induced in it by the force which is 
contracting it, by the gravitating force, and this force, so 
far as our evidence goes, is derived nearly altogether from 
the sun. My argument is that the heat of the earth is 
mediately, but not immediately due to the sun’s influence, 
that the sun’s influence causes the earth to contract, and 
that in contracting heat is squeezed out of it. That we 
derive no heat whatever qua heat from the sun, or to use a 
simile, the voltaic battery supplies the electric current 
which induces the magnetism in the iron but does not itself 
furnish the magnetism. 
This at once removes a vast quantity of apparent difficulty 
for wherever the sun beats there it exercises its influence of 
gravity, and the result is invariably an induction of heat, 
so that winter and summer, day and night, are dependent 
for their varying temperature on the sun, although in a 
different manner to that popularly supposed. 
There is another and a more palpable difficulty that 
obtrudes itself at once upon one’s notice in defending the 
position I am arguing for. It is said : surely, if we step out 
of the sunshine into the shade, or vice versa, and exclude 
the radiated heat from the ground we shall find direct evi- 
dence both from our feeling and from the usual effects of 
heat that the sun’s rays are distinctly hot, that in beating 
on our hand, on a moist surface, &c. &c., symptoms of absorp- 
tion of heat at once present themselves — the hand grows 
