372 B. M. Deeleij—Flow of Antarctic Ice. 



In the case of the Great Barrier the ice presents a high vertical 

 face to the sea, and the whole mass is moving from the south at 

 a rate of ahout 600 yards per annum. Now if we place the origin 

 of the Barrier ice, as such, about 400 miles from the seaward face, 

 near where it is fed by the magnificent glacier discovered by 

 Shackleton, the whole of it will have broken off at the sea face and 

 have been replaced in about 1200 years. No portion of it, therefore, 

 can be a remnant, i.e. the remains of the foraier ice-sheet. It has 

 merely become thinner, as the supply of snow falling upon the area 

 became less, and the tributary glaciers became smaller, just as the 

 water-level of a river rises and falls as the rainfall varies. 



The same argument applies to the other more local ice formations. 

 They commence on a hill-side and thicken as they approach the sea, 

 at which they terminate in a vertical face. Now Scott and Ferrar 

 have shown that the sea has a very rapid wasting effect upon the 

 ice which reaches it. The cliff's are undercut and large masses break 

 off. Even the sea ice is being rapidly melted from beneath when 

 the upper surface is below the freezing-point. The vertical face 

 which faces the sea is maintained by the continual motion of the ice- 

 foot towards the sea. 



With regard to the peculiar ice-islands, a photograph of one off 

 King Edward's Land is shown. This I take it is regarded as 

 a remnant of the old ice-sheet. The photograph shows a mass of 

 ice, with an irregular upper surface sloping roughly towards the 

 sea in all directions. It terminates on the sea face in an overhanging 

 cliff of considerable height. May not these ice-islands be rocky islands 

 upon which more snow falls than is melted by the sun ? In such a case 

 the ice-cap would reach a thickness sufficiently great to allow it 

 to discharge the ice seawards. A section would show two wedge- 

 shaped areas terminating in seaward cliffs. In other words the ice- 

 islands are the island equivalents of the shore ice. 



Erom the photographs shown, and the descriptions of the various 

 ice formations, I see no signs of extraordinary stagnation. On the 

 contrary, the ice is everywhere in motion, to judge from the usual 

 signs. 



Ice is a viscous substance — a peculiar one in some respects, it is 

 true. Water, oil, honey, and pitch are also viscous. To ascertain 

 how these substances will act in any case it is necessary to know how 

 viscous they are. The unit of viscosity is measured by the tangential 

 force per unit area of either of two horizontal planes, at the 

 unit distance apart, one of which is fixed while the other moves 

 with unit velocity, the space between the planes being filled with 

 the viscous substance. The viscosity of liquids can be measured in 

 many ways. Thin oils, water, spirits, etc., are best dealt with by 

 measuring their rate of flow through capillary tubes. For thick oils, 

 honey, etc., tubes having larger diameters must be used. Eor pitch 

 the conditions of flow through large holes in thin plates or the flow 

 down troughs give satisfactory results. Eor glaciers, if we know 

 the rate of flow, the inclination, and the width and thickness, the 

 result can be calculated directly. 



The following table gives the viscosity of some liquids : — 



