On Rossett’s Law of Cooling. 425 
for the following excess of radiation above the present radiation 
at 80° N. lat. 
Miocene times : : 19°36 melted feet of ice. 
Jurassic times 3 : 33°46 - re 
Albumen-coagulation ; 70°66 “5 oF 
Let us suppose the earth to bea globe of boiling water, and 
calculate how long she could keep up the foregoing radiations, 
before being converted into a globe of ice. 
Imagine a cone with its vertex at the centre of the earth, and 
its base at 80° N. lat.; the volume of this cone will be, in cubic 
feet— 
4000 x 5280 
ee a me 
Let e be the excess of heat radiated at any geological time, 
above that radiated at present in the same latitude ; and let 1 be 
the number of years before the cone of boiling water is converted 
into a cone of ice; we now have, since the difference between the 
boiling and freezing points is 180° F. and since the latent heat of 
water is 143° F.— 
143 on = 1000 x 5280 x 323 
3 
or 
4000 x 5280 x 323 
Tey ashes i (12) 
From (12) we calculate— 
Lengths of time required to convert the cone of boiling water 
into the cone of ice at 80° N. lat., at the rates of radiation cor- 
responding to 
1 Miocene time : . ° 821,360 years. 
2 Jurassic time : A 475,240 ,, 
3 Albumen-coagulation : : 225,040 ,, 
If we assume, as an approximation to the relative durations of 
geological times, the numbers given at p. 8, and make use of 
the mean of the radiations at the beginning and end of each 
period, we shall find, for the mean radiation at 80° N. lat. during 
