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CORRESPONDENCE. 
*** The Editor does not hold himself responsible for statements of fads or 
opinions expressed in Correspondence, or in Articles bearing the signature 
of their respective authors. 
THE EARTH’S TEMPERATURE, 
To the Editor of the Journal of Science . 
Hypothesis : The heat of the earth is caused by pressure. 
Sir, — Although not aware of it, I am probably not the first to 
attribute the temperature of the Earth — or rather the increasing 
heat thereof — to pressure, or, in other words, to maintain that 
the weight of the material above becomes converted into heat 
below, — its only escape ; and, on inquiry into the matter, this 
theory seems amply borne out by fadi : moreover, I am encou- 
raged to lay this view before the world, because on mentioning it 
to an authority in these matters he did not see reason to rejedt 
it, but was not prepared to express an opinion. 
It is almost certainly demonstrated that, after reaching the 
depth of about 50 feet below the surface, the temperature regu- 
larly increases at the rate of i° F. for about every interval of 
60 yards. Thus, if it can be proved that the pressure of a layer 
of rock would produce the same rate of increase, it is very plau- 
sible to infer that this is the cause : this can, I believe, be 
satisfactorily shown. 
Dr. Joules’s statistics of the conversion of mechanical energy 
into heat are, I think, the best to go by. He demonstrates con- 
clusively that if a weight of 1 lb. fall 772 feet, it will raise the 
temperature of 1 lb. of water iP F. His experiment, of course, 
cannot be applied to earth, yet the latter is a material like the 
former, and is under the same laws. Will not the same pressure 
on a pound of water produce the same amount of heat as on an 
equal amount of earth ? Now the foot-pounds to raise a cubic 
foot of water i° F. are 48-250; but diredtly we turn to minerals 
we are at once met with a host of differences in weight. Taking 
Molesworth’s Tables we find 150 lbs. per cubic foot about a fair 
average. Pradtically a column of rock 12" X i 2 " = 1 lb., or a 
cubic foot 144 lbs. (Mr. A. Lupton, Yorkshire College), perhaps 
rather more. At the end of the first depth of 60 feet, for i° F., 
2 B 2 
