and of the Planetary Spaces. 65 



ties of temperature of the regions of space traversed by the earth, 

 an infinity of hypotheses which could serve but as examples of 

 calculations, proper only to show how these inequalities should 

 influence the temperature of the surface of the globe ; and that 

 this influence may be sensible it is only necessary that the con- 

 secutive Tnaxinium and minimum of the heat of space differ 

 widely, and that they be separated by very long' intervals of time. 



According to the example which I have arbitrarily chosen in 

 my work, the temperature of space, in one million of years, would 

 pass from + 100° to — 100*^, and return again from - 100° to 

 + 100° ; and if we should farther suppose that it is now at its 

 m,inim,u7n, an increase of the temperature of the earth, in a ver- 

 tical direction, from the surface towards the centre, very nearly 

 equal to that we observe would be the result. This increase will 

 be sensibly uniform, at all accessible depths : it will vary beyond ; 

 and at a depth of about 7000 metres the temperature of the globe 

 will attain its maximum; and surpass, by about 107° that of the 

 surface : beyond this it will diminish, so that at about 60,000 me- 

 tres from the surface the influence of the inequalities of the tem- 

 perature of space will have entirely disappeared. In the same 

 example the temperature of the surface of the globe, 5,000 cen- 

 turies since, would have surpassed that of the present day little 

 less than 200°, and it will again be the same when another 5,000 

 centuries shall have elapsed ; a temperature that must have ren- 

 dered, and will again render the earth unhabitable to the hu- 

 man species : but 500 centuries before, and 500 centuries after 

 the period in Avhich we live, the temperature of the surface would 

 not exceed, by more than about 5°, that which we now witness. 



Such is, in my opinion, the true cause of the augmentation of 

 temperature which we experience upon each vertical line, from 

 the earth's surface, towards its centre, in proportion to the dis- 

 tance from that surface. In this theory the mean temperature of 

 the superficies varies with extreme lentitude, but incomparably 

 less than the portion of temperature which might be due to prim- 

 itive heat, if that was still sensible. Farthermore, this variation 

 is alternative, and thus is able to concur to the explanation of the 

 revolution to which the exteriour layers of the globe have been 

 subject ; while, on the contrary, such portion of the temperature 

 as might be due to the other cause diminishes constantly, and 

 this without alternation. If the increased temperature observed 



Vol. XXXIV.— No. 1. 9 



