On Rossetti’s Law of Cooling. 427 
At present, at 80° N. lat., we have 
H=A41°9 feet of ice. 
0=4-5° F, 
__0-2489 
~ (4602 
a=160-5° F. 
In Miocene times 
H=A41°9 (by hypothesis) 
@=44:3° 
ny Gi 2489 
60)? 
From these data, we find by equation (9), the value of a in 
Miocene times 
a=95°76° F 
In like manner, we find the value of a, corresponding with 
6=68:7° F (jurassic), and 6=122-0° F. (albumen coagulation) ; and 
finally, 
The temperature of the Heat-inclosure, depending on atmospheric 
conditious, necessary to produce the requisite Geological 
Climates, independent of any increase of Sun-heat or Earth- 
heat at 80° N. lat. 
Present time ‘ F ; 4.160°50° F, 
Miocene ,, 5 3 A + 95°76 ,, 
Jurassic ,, : : + 58°73 ,, 
Albumen-coagulation time 5 — 16°84 ,, 
The positive values are reckoned Aelow zero of Fahrenheit, 
and the negative values are reckoned above zero. 
It is very unlikely, that the thermal constants of the earth’s 
atmosphere have ever changed so much as to convert an inclosure 
of 160°5° below zero into an inclosure of 16°84° above zero, 
through 177°34° F. altogether ; nevertheless, it is quite certain that 
conditions formerly existed in the earth’s atmosphere which 
operated in the direction here indicated, and which may have 
greatly economised the increase of sun-heat required, without 
accounting for the entire change in climate. 
Professor Tyndall* has given the following relative absorptive 
power for heat emanating from a source at 312° F. of various 
gases at the normal pressure of 30 inches, when a column of the 
gas, 4 feet in length was subjected to experiment. 
* Miller’s Elements of Chemistry, part i., pages 338-9, 
