KiJ OX THE SOUHCKS OF HEAT WHICH INFLUENCE CLIMATE. 



th'.'ii, as a circumstance nearly completely proved, that the earth possesses a heat 

 of its own, independent of what it receives from the sun, and being the remains 

 of its original heat. This return to ideas long since put forth by our greatest 

 men, shews that it is never safe to slight even the boldest conjectures of men of 

 genius ; it is one of their privileges that truth often appears to them in their 

 dreams." Since we then have a central temperature sufficient to fuse all the 

 materials we meet with on the earth's surface, it must necessarily follow that the 

 mass of heated matter in the centre is in a fluid or incandescent state — unless 

 we can shew that the enormous pressure which can be demonstrated to exist on 

 the matter in the interior of our planet retards or prevents its fusion. There is 

 no chance of our being able to experiment with matter under a pressure any 

 thing at all approaching that to which it must be subjected at depths consider- 

 ably below the earth's surface. No experiments, that I am aware of, go to prove 

 solid matter to be of more difficult fussion when under a heavy superincumbent 

 weight ; but the certain knowledge of the existence of these great pressures 

 inclines me to the belief that matter may there possess properties of which we 

 know nothing. 



It can be demonstrated that the attraction at any point within a sphere of 

 equal density, or of successive concentric strata of uniform but unequal densities, 

 is always as the distance from the centre. Therefore the whole pressure of a 

 column of homogeneous matter from the circumference of the earth to its centre, 

 will be half what the same pressure would be if the attractive force were uniform 

 throughout. This will give for matter of the mean density of our planet a force 

 equal to a million and a half atmospheres exercised by the superincumbent mass 

 at the earth's centre. Water at the centre would be under a pressure of 330,000 

 atmospheres. Such a force might retain it as a solid, though even at a high 

 temperature ; but here, also, we are left to conjecture, as we have no experiments 

 made on fluids under great pressures to guide us. 



Arago and Dulong have given an empirical formula for ascertaining the 

 temperature at which water begins to assume a gaseous state under pressure. 

 This is verified by experiment only so far as 5| atmospheres ; there is therefore 

 a difficulty in extending it to great weights ; the furthest it has been attempted 

 by its authors is to 1,000 atmospheres, where it may not greatly err. Water at 

 the depth of six miles below the level of the sea is nearly under this pressure, 

 though Arago's formula shews that it will require a temperature above a red 

 heat, and higher than that of melted Zinc, to bring it to the boiling point. This 

 sufficiently demonstrates how different may be the state of matter at depths in * 

 the earth from what we know of it on the surface. 



The late Sir John Leslie concluded, from an inquiry into the elasticity of solid 

 bodies, that at a distance of a few miles below the earth's surface, a specific 



