446 Climate of the Glacial Period. (October, 
than a place under exactly the same conditions, where a 
thermometer exposed to the rays of the sun would register 
the same amount of heat received, but where the sun rose 
and set every twelve hours, so that the heat by day and the 
cold by night were never so excessive. 
Thus, if we suppose the earth’s axis to have been 
originally perpendicular to the plane of its orbit, so that it 
had twelve hours’ night and twelve hours’ day all over the 
world, and that from some cause or other the axis began 
to incline and the inclination gradually to increase, the 
seasons of the year in the temperate and arCtic zones would 
tend to become more and more distinét. An ever-widening 
circle around the poles would be covered by snow during 
the cold winter, and lower the temperature of the summer 
by reflecting the rays of the sun as long as it lasted; and 
if the obliquity increased to a greater amount than at 
present, so would a greater area be brought under aré¢tic 
conditions, and an approach be made to the cold of the 
Glacial period. 
The accumulation of snow is dependent on another faétor, 
namely, increased precipitation ; and I doubt if any theory 
would satisfy the conditions of the case that simply increased 
the cold of the glaciated regions without providing for an 
increased evaporation outside these regions, and thus to 
allow greater precipitation upon them. An increase of the 
obliquity of the ecliptic satisfies this condition, for whilst 
on one hand the ar¢tic circle would be extended, so on the 
other would the tropics; one part of the temperate zones, 
that next the poles, would have its mean temperature 
greatly lowered; whilst the other, that nearest the equator, 
would have its temperature raised and become an evapo- 
rating area. Thus, supposing Lieut.-Col. Drayson to be 
right in his theory, that at one time the obliquity was 
as much as about 353°, the arc¢tic circle would then reach 
to latitude 543°, and the tropics to 353°, reducing the 
temperate zones from their present width of 43° each to 
only 19°, one-half of the decrease being added to the arétic 
circle and one-half to the tropics. As soon, also, as the 
ice had extended so far as to shut off the warm currents 
of the ocean that penetrate nearly to the pole, much 
of the heat now spent in melting the ice of the ar¢tic circle 
would be expended in evaporation, and precipitation would 
be proportionally increased. 
Those who have followed me in this short argument will, 
I believe, admit that an increase of the obliquity of the 
ecliptic does appear to be sufficient to cause an addition to 
