CONDUCTIOX AND P.ADIATIOX. 147 



parts, anil constantly flows towards the polar regions, by winch it is 

 emitted into the planetary spaces. 



Climate is affected by man}- thermotic influences, besides the con- 

 duction and radiation of the solid mass of the earth. The atmosphere, 

 for example, produces upon terrestrial temperatures effects which it is 

 easy to see are very great ; but these it is not yet in the power of cal- 

 culation to appreciate ; 14 and it is clear that they depend upon other 

 properties of air besides its power to transmit heat. We must there- 

 fore dismiss them, at least for the present. 



3. Temperature of the Interior of the Earth. The question of the 

 temperature of the interior of the earth has excited great interest, in 

 consequence of its bearing on other branches of knowledge. The 

 various facts which have been supposed to indicate the fluidity of the 

 central parts of the terrestrial globe, belong, in general, to geological 

 science ; but so far as they require the light of thermotical calculations 

 in order to be rightly reasoned upon, they properly come under our 

 notice here. 



The principal problem of this kind which has been treated of is this : 

 If in the o'lobe of the earth there be a certain original heat, result- 



o ~ 



ing from its earlier condition, and independent of the action of the sun, 

 to what results will this give rise? and how far do the observed tern- 



o 



peratures of points below the surface lead us to such a supposition ? 

 It has, for instance, been asserted, that in many parts of the world t!i" 

 temperature, as observed in mines and other excavations, increases in 

 descending, at the rate of one degree (centesimal) in about forty yards. 

 What inference does this justify .' 



The answer to this question was given by Fourier and by Laplace. 

 The former mathematician had already considered the problem of the 

 cooling of a large sphere, in his Memoirs of 1807, 1809, and 1811. 

 These, however, lay unpublished in the archives of the Institute for 

 many years. But in 1820, when the accumulation of observations 

 which indicated an increase of the temperature of the earth as we 

 descend, had drawn observation to the subject, Fourier gave, in the 

 Bulletin of the Philomathic Society, 15 a summary of his results, as tin- 

 as they bore on this point. His conclusion was, that such an increase 

 of temperature in proceeding towards the centre of the earth, can aris< 

 from nothing but the remains of a primitive heat ; that the heat 

 vhich the sun's action would communicate, would, in its final and 



14 JKm. Inst. torn. vii. p. 584. 1B Bullet, des Sc. 1820, p. 58. 



