364 
Correspondence . 
[June, 
we reach the depth of 330 feet (50 -f 60 yards). Multiply 
330 X 144 = 47,720, a figure which, all sides considered, is iden- 
tical with Dr. Joules’s, and from a perfectly different source. 
May we not say, then, that the actual state of the heat of earth 
agrees with the theoretical hypothesis and Dr. Joules’s experi- 
ments, and that the heat is due to the pressure. No one denies 
that pressure does produce heat ; even so light a thing as air 
is found to be heated by compression with its own weight at the 
bottom of a pit’s shaft ; and air, if compressed strongly enough, 
will ignite tinder, as most people know, — then why not earth ? 
It may be argued that this would uphold the theory of the 
fluidity of the earth’s interior, but seemingly we are as much in 
the dark as ever. For if we consider the earth as made up of so 
many concentric hollow spheres, fitting one inside another, we 
„can see that the weight, or gravity, is really concentrated in the 
inner side of the globe, and, being circular every way, is self- 
supporting ; so much so that the imaginary resultants will not 
pass beyond the inner surface centreward, and therefore there 
will be little, if any, downward thrust. It is evident, also, that 
there would be a greater weight, side thrusting, &c., in the 
outer sphere than in any of the inner ones ; hence the heat 
would actually decrease (from this cause) towards the earth's 
centre : there must be a limit to compression ; we cannot press 
material that cannot escape anywhere into nothing. Moreover, 
if the world were a mass of fluid in an egg-shell, would not its 
magnetic influence be destroyed, &c. ? We must always look at 
these things with a large, comprehensive view; even in our 
deepest mine we have not even pierced this egg-shell in propor- 
tion, and therefore can draw no indisputable conclusion. 
And finally, why are volcanoes always at the top of mountains ? 
The volcanoes came to the mountains, and not the mountains to 
the volcanoes. This rises many interesting questions which are 
best left till we see whether this stands. — I am, &c., 
David Yewdall Cliff. 
Ilkley, Leeds, May 10, 1881. 
THE FORMATIVE POWER IN NATURE. 
To the Editor of the Journal of Science. 
Sir, — Had it been my intention to criticise the article on “ The 
Formative Power in Nature ” in any adverse spirit, I should 
have affixed my name in full to the letter in your No. for April. 
But my comments on Mr. Billing’s article were far from being in 
opposition to his views, and were designed rather to supplement 
