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 maximum 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 [ 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 
minimum, an increase of the temperature of the earth, in a ver- 
tical Reections, 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 métres the temperature of the globe 
will attain its marimum, 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 which 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 
Vou. XXXIV.—No. 1. 9 
