where w is the angular velocity of the earth's rotation, <p the geographic latitude, c the drift speed, 

 m = (5^ Trr^ h the mass of the floe, 6 the density of the ice, r the radius of the base of the floe and a 

 the height of the floe. 



The hydrodynamic resistance to the movement of the floe can be divided into three parts: 

 1) wave, 2) drag and 3) surface resistance. 



I neglect the wave resistance, since the speed of the ice drift with respect to the water is 

 small. The drag coefficient may be considered proportional to the vertical area cross-section of 

 the underwater part of the floe and the second power of the drift speed of the floe. Since even in 

 the case of icebergs the vertical dimensions of the underwater part are negligible compared with 

 the horizontal dimensions, I have also neglected the drag resistance in the first approximation. 



The surface resistance is also proportional to the surface of the interface water-ice and the 

 second power of the speed. For a cylindrical floe we may consider the surface resistance to be: 



where ttt^ is the area of the base, A is the proportionality factor and c the speed. 

 Substituting formulas (2) and (3) in formula (1), we get 



tan a = ,' ^'l , 2ci)C sin ^ = .4 — sine?, (4) 



where ,4 is a proportionality factor. 



From this formula it follows that 



1. The drift angle of the actual wind drift of the floe is a function of geographic latitude, 

 reaching its maximum at the pole . 



2. The drift angle increases with increasing vertical dimensions of the floe. 



3. The drift angle decreases as the drift speed of the floe increases; since the drift speed of 

 the floe is a function of wind speed, the stronger the wind is, the smaller the drift angle of the floe 

 will be . 



The speed of the actual wind drift of the floe, of course, is a function of the "sail power" of 

 the floe, in other words it is a function of the ratio of the heights of the underwater and above-water 

 parts of the floe. Direct measurements of the actual wind drift of icebergs, made by the 

 International Ice Patrol off Newfoundland, give the following drift speeds of isolated icebergs 

 (table 106) in miles per day, given in cm/sec in parentheses, according to Smith.* 



From table 106 it is evident that Smith considers the true wind drift speed of the ice to be 

 about directly proportional to the ratio of the above-water height of the iceberg to the underwater 

 part and, furthermore, proportional to the wind speed. Taking the average wind force of 4 to 5 to 

 be 7.5 m/sec and a wind of force 6-7 to be 12 .5 m/sec, I computed the wind factors given in table 

 107 on the basis of Smith's table. 



*In this table Smith has ignored the influence of the current. Furthermore, here and else- 

 where in his discussions Smith does not consider the Coriolis force; in other words, he considers 

 the actual drift speed of the ice to be governed by the wind. The last line of the table refers to the 

 wind drift of a vessel off Newfoundland. 



383 



