86 



TEMPERATUEE. 



+vrF 



South Jan. Feb Mar April May June Jury Aug Sep Oct. Nov. Dec Jan. Feb Mar April May June July Aug. Sep Oct 

 NoflTM July Aug Sep Oct No^. Dec. Jan. Feb. Mar April May June July Aug Sep. Oct. Nov- Dec. Jan. Feb. Mar. April 



Fig. 29. Temperature and Insolation. 



(r) The temperature in the north oscillates about a mean temperature 18°r. higher 

 than that over the Barrier, and as the amplitude of the oscillation is greater 

 in the north than the south, the maximum temperature in the north is not only 

 higher than in the south but is several degrees above the freezing point. 



Before we can explain these differences, it is necessary to understand the local conditions 

 to which the observations refer. We have already described the surroundings of the Barrier. 

 The temperature curve refers to that part of the Barrier between One Ton Camp in 79|° S. 

 and the southern coast of Ross Island. The mean latitude is somewhat greater than 78° 

 to which the other curves refer, but the difference is so small as to be immaterial for our 

 discussion. 



The temperature curve for the north does not refer to any one locality, it is based on 

 the mean temperature of latitude 78° N. A glance at the map of the north polar region 

 will show that this latitude, except where it crosses Greenland, runs almost entirely over the 

 Polar Sea, approximatsly 80 per cent, lies over water and 20 per cent, over snow-covered 

 land. An important point is that within this circle of latitude practically the whole area is 

 a permanently frozen sea, while the great continental masses of Asia and North America 

 surround it on the outside for nearly three-quarters of its circumference. 



During the greater part of the year the sea along latitude 78° N. is itself frozen, but 

 during the summer there are occasionally breaks in the ice through which the open water 

 comes to the surface. 



It is a well-know-n fact that owing to the large heat capacity of water it warms up 

 slowly during spring and summer and cools slowly during the autumn and winter. Haun has 



