Voltaic Induction. 23 



be much greater as we advance further into the interior. These 

 considerations would explain to us (even if the exterior refrigeration 

 during winter does not already do it) why M. Scoresby found a 

 slight increase of temperature at increasing depths in the sea be- 

 tween Greenland and Spitzbergen, the ground of these two masses 

 of land, and indeed the bottom of the sea between them, being en- 

 tirely volcanic. 



These same considerations discover to us the possibility of a dif- 

 ference of proper heat between one place and another, at the depth 

 where the thermometer is stationary upon the continents ; thus the 

 thermometric observations given in the tables at the commencement 

 of our first chapter, show very palpable differences, at depths where 

 all influence of climate ceases, and which can be attributed only to 

 local circumstances. But as we know no other causes than those 

 just expressed, and as these suffice to account for the phenomena, 

 we think we have solved in all its points, the problem which consti- 

 tutes the subject of this chapter.* 





Art. III. — An Enquiry into the Cause of the Voltaic Currents pro- 

 duced by the action of magnets and electro-dynamic cylinders upon 

 coils and revolving plates ; by John P. Emmet, M. D., Prof, of 

 Chemistry in the University of Virginia. — Jan. 1834. 



Every person, conversant with the history of electro-magnetism, 

 knows how long it was before it became satisfactorily proved that 

 magnetism constantly accompanies the voltaic current j and, that af- 

 ter Oersted furnished, by a highly important discovery, the most con- 

 clusive evidence, it was nearly six years before he arrived at satis- 



* The partisans of the system of an incandescent globe would perhaps attempt to 

 explain these irregularities of temperature by the difference of conducting power of 

 the different rocks, and of their appendages. But it will be immediately perceived, 

 first, that this explanation will not apply to observations in places near each other, 

 as two pits in one and the same mine, and it will not agree with the results which 

 M. Fourier has drawn from his calculations, relative to the extreme slowness with 



* 



which heat advances at present from the depth of 30 leagues to the surface . In or- 

 der to obtain, at the depth of some hundred metres, the remarkable differences of 

 temperature, and the increase of temperature at the same level, it is necessary that 

 the cause of heat should be incomparably nearer these points than would be the in- 

 candescent globe ; and it is on these accounts that we present the causes of heat 

 that have just been enumerated. 



