PRELIMINARY DISCOURSE. 5 



From what characteristic can we ascertain that the earth 

 has not entirely lost its original heat; and what are the exact 

 laws of the loss ? 



If, as several observations indicate, this fundamental heat 

 is not wholly dissipated, it must be immense at great depths, 

 and nevertheless it has no sensible influence at the present time 

 on the mean temperature of the climates. The effects which 

 are observed in them are due to the action of the solar rays. 

 But independently of these two sources of heat, the one funda 

 mental and primitive, proper to the terrestrial globe, the other due 

 to the presence of the sun, is there not a more universal cause, 

 which determines the temperature of the heavens, in that part 

 of space which the solar system now occupies? Since the ob 

 served facts necessitate this cause, what are the consequences 

 of an exact theory in this entirely new question; how shall we 

 be able to determine that constant value of the temperature of 

 space, and deduce from it the temperature which belongs to each 

 planet ? 



To these, questions must be added others which depend on 

 the properties of radiant heat. The physical cause of the re 

 flection of cold, that is to say the reflection of a lesser degree 

 of heat, is very distinctly known ; but what is the mathematical 

 expression of this effect ? 



On what general principles do the atmospheric temperatures 

 depend, whether the thermometer which measures them receives 

 the solar rays directly, on a surface metallic or unpolished, 

 or whether this instrument remains exposed, during the night, 

 under a sky free from clouds, to contact with the air, to radiation 

 from terrestrial bodies, and to that from the most distant and 

 coldest parts of the atmosphere ? 



The intensity of the rays which escape from a point on the 

 surface of any heated body varying with their inclination ac 

 cording to a law which experiments have indicated, is there not a 

 necessary mathematical relation between this law and the general 

 fact of the equilibrium of heat ; and what is the physical cause of 

 this inequality in intensity ? 



Lastly, when heat penetrates fluid masses, and determines in 

 them internal movements by continual changes of the temperature 

 and density of each molecule, can we still express, by differential 



