536 HISTORY OF THERMOTICS. 



ing the extent of the future cooling of the surface, 

 which it was shown must be insensible. Everything 

 tended to prove that, within the period which the 

 history of the human race embraces, no discoverable 

 change of temperature had taken place from the 

 progress of this central cooling. Laplace further 

 calculated the effect 16 which any contraction of the 

 globe of the earth by cooling would produce on 

 the length of the day. He had already shown, 

 by astronomical reasoning, that the day had not 

 become shorter by 1 -200th of a second, since the 

 time of Hipparchus ; and thus his inferences agreed 

 with those of Fourier. As far as regards the 

 smallness of the perceptible effect due to the past 

 changes of the earth's temperature, there can be no 

 doubt that all the curious conclusions just stated 

 are deduced in a manner quite satisfactory, from 

 the fact of a general increase of heat in descending 

 below the surface of the earth ; and thus our prin- 

 ciples of speculative science have a bearing upon 

 the history of the past changes of the universe, and 

 give us information concerning the state of things in 

 portions of time otherwise quite out of our reach. 



4. Heat of the Planetary Spaces. In the same 

 manner, this portion of science is appealed to for 

 information concerning parts of space which are 

 utterly inaccessible to observation. The doctrine of 

 heat leads to conclusions concerning the tempera- 

 tures of the spaces which surround the earth, and in 

 16 Conn, des Terns, 1823. 



