INTRODUCTORY CHAPTER . 
33 
maximum height in the sky. During the midsummer 
months the sun would acquire considerable heating 
power, and this power would be so constant, and free 
from diminution by nocturnal cooling, that the land 
and waters would become warmed, and would ab¬ 
sorb heat. This heat would be gradually liberated 
later in the year. The local distribution of heat would 
be modified by the nature of the ground, the height of 
land, and the distribution of sea and land ; but it is 
theoretically probable that at the Pole the mean tem¬ 
perature of the air in July and August is much higher 
than it is generally thought to be. During the winter 
the continuousness of the night would equally favour 
a very low temperature, so that probably the range of 
temperature in the circumpolar area is greater than in 
any other part of the globe. Evidences of high sum¬ 
mer temperature are not entirely wanting. Many of 
the most northern coasts reached are strewed with 
drift-wood, and even trunks of trees, which in many 
cases appear to have come from the north. A list of 
the species thus occurring would throw light upon the 
probable localities where they grew. Again, streams 
or outflows of warm water from the Pole have been 
observed in many localities. 
These, wherever met with, are commonly assigned 
to the Gulf Stream; but as will be noted in a subse¬ 
ts 
