ON THE SOURCES OF HEAT WHICH INFLUENCE CLIMATE. 461 



but after admitting the existence of central heat, it will be seen that much doubt 

 prevails as to its intensity, and still more to the existence of a large mass of 

 fluid matter. 



The difficulties of the experimental inquiries will be well illustrated by citing 

 those of M. De La Reeve. At G80 feet below the surface he found, in the first 

 instance, an increase of 22 degrees of Fahrenheit above the mean of the climate ; 

 continuing his experiments until he obtained constant and uniform results, the 

 amount of elevation of temperature was reduced to 13| degrees for 680 feet; and 

 the great error of 8| degrees was solely due to a small quantity of air lodged in 

 the upper part of the cylindrical case containing the thermometer. This air 

 was much compressed as it descended, from the pressure of the superincumbent 

 column of water ; and its latent caloric evolved. M. Cordier also found, in 

 mines not two miles apart, that the rate of increment of temperature varied 

 exceedingly, being nearly double in one mine what it was in another. This 

 might be partly due to the many sources of error to which experiments made in 

 mines open to the atmosphere are subject, but M. Cordier, fully aware of these, 

 used his best exertions to avoid them. De La Reeve's experiments, conducted 

 with much exactness, and persevered in till various sources of error were dis- 

 covered and removed, are worthy of great confidence. He found the increase 

 to advance strictly by an arithmetical progression ; he gives it at 1^ degrees, 

 Fahrenheit, for every 100 feet, being not so rapid as the mean augmentation of 

 temperature assigned by M. Cordier, whose results were one degree, centigrade, 

 for 15 metres in France, and one degree in every 25 metres for the earth's surface 

 generally. 



If we admit the experiments of M. De La Reeve, confirmed by those of 

 Arago, Fox, and many others, to prove an increase of temperature to proceed on 

 an arithmetical ratio, as we descend below the earth's surface, the heat will 

 ultimately reach a point sufficient to fuse all the materials with which we are 

 acquainted. The spheroidal form of our planet is a strong proof in favour of the 

 primitive incandescence of its mass ; but the fusion and recomposition of certain 

 rocks by any artificial means long stood in the way of this hypothesis, until a 

 distinguished German chemist, M. Mitscherlich, succeeded to fuse the most 

 refractory, and also to recompose, from the substances found in them by analysis, 

 crystals of the same form and character as those that were natural. As Cuvier, 

 in a discourse on the progress of Chemistry, has treated fully of this valuable 

 discovery, with its influence on the theory of central heat, I gladly avail myself 

 of the words of this extraordinary man : — " It seems," says he, " almost to carry 

 at last to a rigourous demonstration a celebrated hypothesis, advanced without 

 proof by Descartes, Leibnitz, and Buffon, and to which the recent labours of 

 Laplace had already given a high degree of probability ; we may regard it, 



VOL. III.- no. xxiv. 3 P 



