ABLATION 35 



These ablation results are not very different from the evaporation observations 

 made by the Z^/scorery Expedition.* In these experiments three shallow dishes were 

 employed, giving areas respectively of 12, 12, and 24 square inches. These were 

 filled with water, which was allowed to freeze, and then the dishes were placed on the 

 meteorological screen. The dish and ice were weighed day by day, and the difference 

 between two consecutive weights gave the loss by evaporation. 



From March to October inclusive, in 1903, the total evaporation amounted to 

 2"910 inches, and the evaporation for November of the previous year amounted to 

 0702 of an inch. If this be added to the previous amount the evaporation for the 

 nine months from March to November would be 3 "6 12 inches. The amount of evapora- 

 tion for December, January, and February is wanting, but it appears to one of us 

 (Professor David) that the amount would have been of the order of '8 inch per month. 

 In this case the total annual evaporation would have been about 2-4 + 3'612 = in 

 round numbers about 6 inches. 



It will be noted that in the case of our experiments we employed actual lake 

 surfixces instead of dishes, and that occasionally the lake surfaces were temporarily 

 snowed over. In most cases, however, the snow covering was quickly dusted off 

 them by strong winds, except in the case of Clear Lake, where there was evidence 

 of some irregular lumpy structure developing on the previous even surface of the ice 

 some time subsequent to snowstorms. 



Probably the estimate given of 7 inches as the total annual evaporation at Cape 

 Royds (irrespective of the ice and snow that are lost by actual thawing through heat 

 radiated from sun-warmed rocks) is not an over-estimate. This great amount of loss 

 of ice by evaporation is, no doubt, due (1) to the extreme dryness of the air ; (2) to 

 the consequent intensity of solar radiation ; (3) to the speed of the blizzard winds. 

 This immense evaporation is obviously a fact of the first importance in studying the 

 glaciology of Antarctica, especially when the additional point is borne in mind (and 

 this point cannot be too strongly emphasized) that probably at least 95 per cent, of 

 the surface of Antarctica is covered superficially not with ice but with snow. The 

 great surface offered by snow spicules and flakes in proportion to their volume would 

 greatly accelerate the rate of the evaporation and so increase its amount. For 

 example, we noticed the tracks of sledges or footprints in the snow within a few weeks 

 were left strongly in relief. This may have been in part a mechanical " survival of 

 the fittest," that is, the compressed snow may have resisted the mechanical force of 

 the blizzards better than the loose snow. 



Spiracle Ice or Moss Ice. Another evidence of ice evaporation is to be found in 

 what may be termed spiracle ice. Dr. Mackay first called attention to this on the 

 journey to the South Magnetic Pole area, when the party was crossing the Drygalski 

 Ice Barrier Tongue. This glacier was heavily crevassed, and here and there were to 



* "National Antarctic ExpeJition," 1901-4. " Meteorology," pt. i. published by the Royal Society, 

 London, 1908, pp. 11 and 473-475. 



