accumulations of dust particles and deposits of moraine matter. In the second case, with cold and 

 clear weather all the dark deposits, warmed by the sun's rays, settle beneath and the glacier sur- 

 face becomes snow-white and porous. On it appears ice globules, glassy ice surfaces, ice needles, 

 etc. and thus there is formed a m^icro- relief on the surface of the glacier. Apparently this micro- 

 relief is formed only under conditions when the coefficient of radiational influence is not less than 

 twice as large as the coefficient way micro- relief is formed when the total heat of radiation energy 

 falling on the glacier surface is at least twice as large as the positive heat-exchange with the air. 

 The foregoing is also entirely applicable for sea ice. 



While sailing near the northern coasts of Spitzbergen and Franz Joseph Land where the weather 

 is continually cloudy in summer, the ice appeared dark and dirty. 



This phenomenon explains the exceptional whiteness and sparkle of the ice fields in the early 

 spring in the artic under conditions of very low air temperatures and bright sunny weather. 



The above considerations show what complexities are inherent in the process of thawing of ice 

 from above. The matter is made still more complex by the fact that although there are instruments 

 which permit of very accurate calculations of radiational balance for any point on the earth's surface, 

 there are very few actual observations even at the polar stations and for ice far away from the 

 coasts there are no observations at all. Conditions at the coastal stations are so different from 

 those on the ice far removed from the shore that it is hardly possible to transpose the results of 

 shore observations for the ice of the central parts of the basins without large corrections, which 

 have not yet been determined. 



Still more difficult is the problem of thermal Influence of the air, conditioned by temperature 

 and by the speed of wind. While we may deduce the wind speed from synoptic maps, this Is con- 

 siderably more difficult with respect to the temperature of the air. 



LITERATURE: 77, 91, 93. 



Section 116. Melting of Ice from the Top 



The question of melting of ice from the top due to action of solar radiation and heat absorbed 

 from the atmosphere is extremely complex from a theoretical point of view. No less difficult is the 

 question of finding empirical formulas since we have at our disposal almost no observations of the 

 melting of the ice. Therefore, until something else may be proposed, I consider it possible to use 

 the following very approximate calculation. 



Let / equal the quantity of heat actually absorbed by a unit of ice area in a unit of time, the 

 quantity being made up of the radiational and thermal actions of the air on the ice. Let us suppose 

 that all of this heat is used exclusively in reduction of the thickness of ice. It follows that for a 

 unit of time dT , the heat absorbed by a unit of ice area wUl be equal to fd T. Due to this heat the 

 thickness of ice should decrease by dft. From this we obtain the equation 



fdT = 8.-kdh, (1) 



where Sf = ice density, 



\ = heat of fusion. 



In this formula the quantity of heat absorbed by the upper surface of ice is constantly changing 

 and the fluctuations of this absorption are quite considerable. 



314 



