262 The American Geologist. April, 1892 
uninhabitable, by the fierce extremes caused by concentrating half the 
annual supply of heat into a summer of very short duration, and spread- 
ing the other half over a long and dreary winter, sharpened to an intoler- 
able intensity of frost when at its climax, by the much greater remote- 
ness of the sun,’”* 
Sir Robert would modify the latter part of the foregoing statement of 
Herschel as follows: “In the northern we should have a short but very 
mild winter with a long but very cool summer, 7. ¢., an approach to per- 
petual spring; while the southern hemisphere would be inconvenienced 
and might be rendered uninhabitable by the fierce extremes caused by 
concentrating sixty-three per cent. of the annual supply of heat into a 
summer of very short duration, and spreading the remaining thirty-seven 
per cent. over a long and dreary winter, sharpened to an intolerable in- 
tensity of frost when at its climax, by the much greater remoteness of 
the sun.” (p. 118.) 
The new law which is thus announced is elsewhere stated as follows: 
“Under all circumstances and on either hemisphere 63 per cent. of the 
total heat of the yearis received during summer, so that only the re- 
maining 37 per cent. is left for winter. (p. 119.) * * * They (these 
figures) would remain the same however the dimensions of the orbit be 
altered, however its eccentricity be altered, or in whatever direction the 
plane of the earth’s equator may inte rsect the plane of the earth’s revo 
lution around the sun.” (p. 121.) 
The effect of this modification of the law governing the distribution 
of heat during summer and winter during varying eccentricities of the 
earth’s orbit, cannot fail to greatly modify the conclusions as to the 
climatic effects which varying eccentricity is competent to produce. 
And the author does not fail to make the most of the situation. 
It is calculated that during the time of high eccentricity when the 
summer lasted for 166 days and the winter for 199 (winter in aphelion), 
the ratio between the amounts of heat received daily in winter and in 
summer, is expressed by the figures .68 and 1.38. This difference, it is 
argued, could not fail to produce a glacial epoch. So sure is the author 
of his conclusion that he says, “perhaps it would hardly be an exaggera- 
tion to assert, that even if geologists had not hitherto discovered the 
Ice Age from its records on the globe’s surface, astronomers would have 
demonstrated by calculation that Ice Ages inust have happened, and would 
even now be urging the geologists to go and look for their traces.” (p. 43). 
Sir Robert dissents from some of the conclusions of Croll concerning 
the change in position which the gulf stream would suffer, “as a conse- 
quence of the transference of the glaciation from one hemisphere to the 
> The doctrine of the recurrence of ice epochs, alternating 
with each other in opposite hemispheres, is a necessary result of the 
position taken by the author, The geological evidences of the truth or 
falsity of the hypothesis advocated, are not discussed. 
opposite.’ 
Geological Survey of Kentucky; Report on the occurrence of petroleum, 
; *Herschel. 
