18 METEOROLOGY 



The specific heat of sea water having a sp. gr. of 1'0043 at 175° C. being taken 

 as "980, that of ice may be taken as follows : 



- 18° to - 78° C. -463 



-78° „ - 188° C. -285 



-188° „ - 252° C. -146* 



This appears to be an extremely important point in connexion with the wind circula- 

 tion on the Magnetic Pole Plateau, and one which has not yet been properly 

 emphasized in glaciological works. In other words, ice would heat up under 

 the sun's rays, at the prevalent Antarctic temperatures, at about twice the rate of sea 

 water, and in the greater cold of winter, so long as it was exposed to the sun, at 

 a considerably increased rate. This would, of course, tend to raise air temperatures 

 by day over the plateau, and so check the plateau wind which springs up so 

 regularly during the night. As soon as the increasing heat of the sun towai'ds noon 

 had sufficiently warmed the snow to make the temperature of the air In contact with 

 it approximate to that of the air over the water of Ross Sea, the i^lateau wind 

 ceased. 



At night the snow of the plateau parted readily with its heat, and the air above 

 it became chilled and heavy, and commenced to flow seawards as the plateau wind. 

 Hence the much greater daily range of temperature on the plateau than alongside of 

 the open waters of Ross Sea. 



At Cape Ptoyds in December the daily range in temperature was about 5° Fahr. 

 At the Drygalski Ice Barrier close to the open water at Relief Inlet the temperature 

 was even more constant between night and day when neither the plateau wind 

 nor the blizzard winds were blowing. On the plateau, the daily range of tem- 

 perature dui'ing the end of December and January was of the order of about 

 20° Fahr.f 



The specific heat of basalt at 12° — 100° C is '1996, as compared with that of ice at 

 — 18° to — 78° C. of "463. It is possible that, to a less extent of course, a similar 

 phenomenon takes place with snow crystals on the plateau. Ice does not readily 

 thaw in the sun's rays when the temperature of the air is below freezing-point 

 on account of the I'elatively rapid conduction of ice, cold from the lower layers of ice 

 being quickly transferred to its upper surface when slow convection currents are set 



* "Smithsonian Pliysical Tables," p. 230. 



t We had no minimum thermometer with us on our journey over the Magnetic Plateau. The small 

 spirit minimum thermometer did not work satisfactorily. Hence there are no records of the temperatures 

 between 11 p.m and about 5 a.m., so the above figure is only approximate. At the same time the figures 

 are the average of a considerable number of daily readings with a sling thermometer, and so are fairly 

 reliable. This comparatively low specific heat of ice also suggests a reason for the rapid sublimation of the 

 snow, and possibly for even a slight thawing below its surface, in the direct rays of the sun on the plateau, 

 at a time when the general air temperature was far below thaw point. On the slopes of Erebus at about 

 9000 feet above sea level, on March 10, 1908, when the shade temperature was about 0° Fahr., the black 

 rocks were quite warm to the touch, and the snow around them was melting r.-ipidly. 



