temperature of the interior of the earth. 1 29 



cd to the very simple proof which it could not have resisted, viz« 

 the comparison of the masses of water with the earthy and me- 

 tallic masses which enter into the composition of our globe. It 

 would be easy to establish that the weight of the whole mass of 

 water, does not exceed a fifty thousandth part of the weight of 

 the whole globe. Acuate the solvent power of this aqueous 

 fluid as you please, it is impossible to make one kilogramme of 

 water dissolve fifty thousand kilogrammes of earthy and metallic 

 matter. 



" We must be permitted to say, that we have not been brought 

 back to the theory of a central fire by any spirit of system, but 

 in opposition to system, and in spite of prejudices. The force 

 of fact has produced this change of opinion ; it results from con- 

 siderations carefully reflected on, and from phenomena of a very 

 diflerent order. Above all. we cannot believe that it is by mere 

 accident that natural philosophy, astronomy, and geology have 

 arrived at the same point by such different routes. We may 

 therefore without hazard assert that an hypothesis equally ne- 

 cessary to all these sciences seems to put on the characters of a 

 real and fundamental principle ; and we may expect it will, by 

 and by, have as happy an influence on the theory of the earth, 

 as the great principle of gravitation has had on the theory of 

 planetary motions. 



" At this point of our knowledge, it should seem that the Acad- 

 emy ought not to remain a stranger to so great a question. 

 Perhaps it is now time to follow up a measure proposed on the 

 28th November, 1825, by M. de la Place.* Perhaps it would be 

 proper also to engage the cooperation of all our scavans by dis- 

 tributing the elements of the question as subjects for prize. The 

 Academy was occupied during the whole century in determining 

 the figure of the earth. An investigation of the principle that 

 presides over the structure of our globe, and governs all the phe- 

 nomena belonging to it, is not less worthy of the efforts of the 

 Academy, nor beneath the means at her disposal. The end pro- 

 posed is certainly among the grandest upon which hnman inge- 

 nuity can exercise itself; and success would be interesting to the 

 whole body of science. If the earth be not that inert mass 

 which it has long been supposed to be, if the appearance of in- 

 ertia be solely ascribable to the slow development of the phe- 



* The proposal was, to name a committee of six members, Messrs. La 

 Place, Arago, Poisson, Thenard, Gay Lussac, and Dulong, to draw up a pro- 

 gramme of experiments to be executed : so that the Academy might determine 

 by exact experiments — 1. The state of the magnetism of the earth. 2. The 

 pressure and composition of the atmosphere, 3. The heat of the globe, at dif' 

 ferent depths. 



Vol. XV.— No. L 17 



