120 C. EB. Dutton on the Contractional Hypothesis.. 
2. Or take the present surface rate at ;3., of a degree per 
foot, the other conditions being unchanged. The epoch would 
be about 160 millions of years, and below 140 miles the rate of 
increase would be inconsiderable. 
3. Taking Sir W. Thomson’s valuation of x at 400, instead 
of 250, and of the surface rate at ;4.,, the epoch becomes about 
98 million years, and below 150 miles the rate of increase 
would be less than 37'5;. 
4. Take x at 250, and rs at =i, at the surface: the epoch 
would be 2,500 millions of years, and below 600 miles the cool- 
ing may be disregarded. 
That Fourier’s theorem, under the general conditions given, 
unless indeed new evidence can be. brought up to show that 
this ratio is much less than ;4,, and that the present accepted 
mean of ;', to ;’; is the result of unknown perturbations, tend- 
ing to exaggerate its value many times. At present, however, 
the unavoidable deduction from this theorem is that the great- 
possible contraction due to secular cooling is insufficient in 
amount to account for the phenomena attributed to it by the 
contractional hypothesis. 
_ So far the discussion has taken no account of such inequal- 
ities in the process of cooling as have occurred in the form of 
Plutonic action. Our knowledge of this subject, er pie of 
oo most necessary inferences from it could be 
; 1s, in most cases, 
potentials developing new affinities. 
_ ular mobility is possible, these changes may give rise to new 
