80 M. POUILLET ON SOLAR HEAT, 
of equilibrium of diathermanous envelopes applying rigorously 
to the inclosure, whose unknown temperature we have just desig- 
nated by v. 
This temperature v must therefore be such that it may pro- 
duce on the surface of the earth, between the tropics, the mean 
temperature of 27°5, which results from observation. But we 
have seen that the excess of temperature of the globe over the 
inclosure is always deduced from the formula 
, 2-8 
p= Ss: 
t being the temperature of the globe, and 7’ the temperature of 
the inclosure. 
Now, here, the temperature of the globe being 27°°5, and that 
of the inclosure v, we must therefore have 
2—-y 
2—6° 
If we take the value of a’ which thence results, and substitute it 
in the preceding equation, and also for B its value 1°146, we find 
gz 5— i 
P _.2—6 
@ = 1-235 pete 0°489. 
And as the whole of the solar experiments gives J! = 0°35, we 
arrive definitely at the equation 
a’ = 1°008 — 0°748.b, . . . « (5) 
in which the only unknown values are the temperature of space 
t and the absorbing power J, which the atmosphere exercises 
upon the terrestrial heat. 
The greatest value of J gives the lower limit of the temperature 
of space; and since 4 cannot be greater than 1, the temperature 
of space cannot be lower than 
— 175°. 
For d! = 0°3 we should find — 187, and for b, = 0°4 only — 164. 
This lower limit once being found, it is easy to ascertain also 
the superior limit; for it corresponds to the smallest value which 
it is possible to attribute to 6: now the experiments of zenithal 
temperature showing that 4 is necessarily greater than 0°8, it re- 
sults that the temperature of space is less than 
— 115°. 
To determine now the intermediate number, comprised be- 
tween these limits, which represents the true temperature of 
space at the present period, numerous experiments will doubtless 
be requisite, extending to all latitudes and all heights. 
