274 Professor De la Rive 07i Electricity. 



nal variations, corresponding to the apparent motion of tiiis lu- 

 minary, which the direction of the magnetic needle, and the in- 

 tensity of the forces which act upon it, experience. The extent 

 of these variations, in our latitudes greater in summer than 

 winter, and in the hottest period of the day than in the night, 

 seems very favourable to this opinion. But we must not go 

 too far, nor wish to push beyond the limits which propriety war- 

 rants this influence of thermo-electrical currents. 



We are thus forced to return to the theory of M. Ampere 

 for an explanation of the origin of electrical terrestrial currents, 

 and consequently to that of Davy respecting the constitution of 

 the globe. And it may now be enquired, whether this last 

 opinion be of such a nature, that it is impossible to explain with- 

 out it the spheroidal shape of the globe, and the several pheno- 

 mena that are occurring, whether on the surface or beneath it ? 

 This is the inquiry upon which M. Ampere, in his lectures, has 

 thrown out some ideas pre-eminently ingenious, and which M. 

 Roulin has communicated in the Revue des Deux Mondes, 

 tom. iii. p. 96.* 



After remarking, that the fact upon which the partisans of 

 the liquidity of the interior of the earth principally rests, viz. 

 the increase of temperature as we penetrate beneath the surface, 

 is not at all contrary to the supposition of the existence of a 

 solid nucleus, exposed at its surface to chemical action, and thus 

 a source of abundant caloric, we cannot but observe that it is 

 almost folly to infer from what occurs in the x j^^o^^ P^^t of the 

 diameter (for no one has ever penetrated a league) what is pass- 

 ing throughout the whole of the extent. On the contrary, it 

 is an unalterable law in physics, that we ought not to consider 

 a law as general, unless it has been clearly observed in the 

 greatest part of the scale ; and assuredly this rule is disregard- 

 ed, when we deduce, from observations made within such narrow 

 limits, the conclusion that the temperature goes on increasing 

 gradually to the centre, or at least to this liquid mass. Those 

 who admit this interior fluidity of the earth, seem, moreover, 

 not to have thought on the influence which the moon would ex- 

 ert upon this enormous liquid mass ; an influence which would 

 produce tides, analogous to those of our seas, but far more ter- 



,-;f,jRjevu^ des Deuj^ Moiides, tom. iii. Second Series (Ir. Juillet 1833), p.9(». 



