On Rossettr’s Law of Cooling. 421 
The mean result of Pouillet and Frélich is— 
Temperature of Space, — — 212°9° F. 
The term temperature of space requires definition, for in one 
sense it is absurd, because we do not believe in any material 
particles existing in interstellar, or even in interplanetary space, 
capable of receiving and emitting heat. I think that the term 
star-heat expresses better what we really mean by the tempera- 
ture of space. 
Notwithstanding the high authority of Pouillet, and his in- 
genious attempts to defend his result, there exists a very general 
scepticism on the subject.* 
if Pouillet had used the term star-heat, he would have been 
astonished at his own result, viz., that the mean annual heat 
received by the earth from the sun would melt a sheet of ice- 
covering equal to 101°7 feet; while in the same time the space- 
temperature, or star-heat, would melt an ice-covering equal to 
85'3 feet ! 
Inside any planetary system, the central star or sun must be 
the chief source of heat, and the effect of the remote stars not 
appreciable ; and in the space midway between any two stars or 
suns, the temperature of a body, if placed there, must fall to the 
absolute cold, or 460° F. below zero.t 
In order to discuss the question of geological climates, let us 
return to the equation (8), or 
H=a (0 +a) (0+ A)?. (9) 
in which H denotes the annual heat received and radiated ; a, a 
coefficient depending upon the radiating surface ; a, the tempera- 
ture of the “heat-inclosure,” including space-radiation, and the 
“convection” and “ conduction” of the atmosphere ; 9, the mean 
annual temperature of the place of observation; and A=460° 
below zero of Fahrenheit, or the temperature of absolute cold. 
* Pouillet observes that to us the sun occupies only five-millioneths of the celestial 
vault, whereas the space-temperature, or rather star-heat, acts over the whole vault. To 
this it may fairly be replied, that as the visible stars appear to us as mere points, the 
whole of them put together would not form the sun’s disc, and that they are indefinitely 
farther off. 
+ Derived from the well-known relation between pressure, volume. and temperature of 
gases, which in Fahrenheit units, gives the equation; 
yu nN 
4604+9 460+0' 
