650 “ Solar Light and the Earth's A tmosphere [November, 
perhaps a curious faCt only, but in what it implies of prac- 
tical moment.” 
“ We deduce in connection with it a new value of the 
solar heat, so far altering the old estimates that we now find 
it capable of melting a shell of ice 60 yards thick, annually, 
over the whole Earth,” &c., “ and we have found that the 
total loss by absorption from the atmosphere is nearly double 
what has been heretofore supposed.” 
Pouillet found that solar heat might annually melt 
30*87 metres of ice, but that this was not all the heat re- 
ceived from without ; he attributed the surplus to space, and 
made it equivalent to melting 26 m. of ice. He therefore 
estimated all heat we annually receive from without equal 
to melting 56*87 m. 
Pouillet took 75 0 C. for the specific heat of ice melting ; 
Prof. Langley, 79*25°. By applying 75° his 54*87 m. increase 
to 57*7 m. The two observers differ, therefore, not as to the 
quantity, only as to the sources of heat. 
In September, 1882, a volume “ On some Properties^ of 
the Earth ” (1880) was presented to Prof. Langley. The 
portion specially pointed out to him discusses the papers of 
Pouillet. The quotation of a few passages sufficiently tells 
the result of the discussion. 
Page 167. — “Apart from other considerations the 30*87 m. 
are slightly in default, because based on r, not on r + h, &c., 
as e is not = 0.” 
Page 175. — “ Pouillet finds that solar heat could annually 
melt an ice-crust of 31*34 m. all over the Earth ; but as 
each point of its surface is in the mean only exposed half 
the day to this aCtion, the heat which enters by it will 
possess double the energy calculated, or that of — 
6*44° x 2 = 12*88. 
He also saw that a larger quantity of heat than 6*44° daily 
must be received from without by any one square centimetre, 
or, putting it differently, by any one point of the Earth ; 
and he saw the source of this heat in space, and calculated 
its energy equal to melting 26 m. of ice.” 
“ He does not claim absolute correctness for his 26 m., 
which are to 31*34 m. as 5*22° : 6*44°. I intend to show 
that this heat is also solar, and is starting from the 
limits of the atmosphere also equivalent to 6*44°, or 6*55° 
considering refraction. If I be right, the effeCt exercised 
on any point of the Earth at the limits of the atmosphere 
will be in the mean of the day equivalent to — 
6*44° x 2 = 12*88°, 
