VERTICAL DISTRIBUTION OF TEMPERATURE IT 



base at about 7000 feet above sea level, and spreading thence downwards over the 

 snow-covered lava sheets to a level of about 3500 feet. Such tendencies to inversion 

 of temperature as one ascends mountains are of course common at the beginning of 

 and during winter, serving to emphasize the fact that during winter the earth's 

 atmosphere cools from the base upwards, and not from above downwards. These 

 conditions obviously tended to unduly raise the snowfall near Cape Royds, where the 

 warm air from off the sea met the cold air descendinsr from Erebus. The average 

 fall of atmospheric temperature from sea level to the top of Erebus is about 1° F. per 

 400 feet, which is not very different from the gradient in temperate latitudes, though 

 of course the grade is less steep. It is suggested that the lessening in the rate of 

 fall of temperature may have been due In part to the strong N.W. air cui'rent which 

 swings, during a blizzard, into a N. and S. direction. This must have been blowing 

 for some time over the top of Erebus during the furious blizzard of March 8, the day 

 before we reached the crater. Such a high-level wind blowing from northern 

 latitudes would of course be warmer than the normal W.S.W. wind which sweeps 

 from off the continental plateau over Erebus. As regards the evidence of vertical 

 distribution of temperature obtained on the joui'ney of the Northern party to the 

 Magnetic Pole area data are wanting for accurate comparison, on account of our 

 distance from the base at Cape Royds, where the check temperatures were taken 

 (about 400 miles at the maximum limit). Thus we can form only a rough idea from 

 the temperatures at our base at Cape Royds what the temperatures at sea level 

 on our route were likely to have been.* 



In considering the distribution of temperature on the Magnetic Pole Plateau one 

 must remember, that in advancing from the coast inland one has first to cross the 

 block mountains of the coastal horst, and in these mountains, in summer time, a 

 considerable amount of dark rock is exj^osed to the sun and absorbs its heat rajs. 

 At the back of this horst the plateau rises in a distance of about 180 miles to about 

 7350 feet above sea level. On account of the difference in specific heat between land 

 and water, together with the absence of convection currents in the rock material of 

 the land,t there is a considerable difference, in summer time, between the tempera- 

 ture of the sea water, and that of the rocks of the adjacent horst. Hence the 

 air over the horst, by day especially, becomes warmer than the air over Ross Sea. 

 The difference in specific heat between ice and water would have the same effect. 



* The temperature obtained by Bernacchi for Cape Adare, at sea level, at 330 miles N.N.E. of Mount 

 Nansen, are for another year (1903-4), but give one some idea as to what increase of temperature to adopt 

 on our base temperatures at Cape Royds. Wo also have our own observations on the sea ice for over 200 

 miles N. of Cape Royds, 1908-9, as a check, as well as the temperatures taken by the Nimrod on her 

 second outward voyage through Ross Sea. During part of this time she was locked in the ice-pack at the 

 time that we were ascending the Magnetic Pole Plateau. 



t The specific heat of water at 15° C. being taken as 1-000, the specific heat of granite, of which 

 most of the exposed rocks of the plateau are composed, may be taken as 1 92 at 12 - 100° C. (" Smithsonian 

 Physical Tables," pp. 229-231.) 



C 



