AS OBSERVED IN THE WEDDELL SEA. 
817 
there are hardly enough observations available, and Such as there are, are for the. 
most part valueless, owing to the observer seldom specifying in detail what type 
of ice he saw. For the present not much can be done to amplify the various pack- 
edges set down on the chart accompanying Mill’s Siege of the South Pole beyond 
adding the Filchner and Shackleton conditions. Such a map to be useful 
should, of course, have the day and month as well as the year inserted, as the edge 
is continually moving northwards. The only data as to the rate of this movement 
are supplied by the Deutschland, which drifted 6 sea-miles a day, and the Endurance, 
nearer the coast, which averaged 4 sea-miles a day. 
IY. — Changes in the Ice. 
From its very beginning the history of the pack-ice was one of continual, 
unceasing change. The field itself was never at rest. Driven by wind and current, 
it was cracked the one day, and compressed the next. Outwardly, therefore, it 
finally appeared very different from the original sheet of young-ice, which consisted 
either of black-ice covered with ice-flowers or of cemented pancakes. Its surface 
became a maze of hummocks and pressure ridges, for the most part drifted over with 
snow. These were the outward signs of change due to its being in motion ; but 
inwardly the ice had also become very different, independently of whether it moved 
or not. It had altered in chemical constitution, in density, structure, hardness, 
elasticity, and so on. These changes, it should be noted, varied greatly according as 
the portion of ice examined was still floating in the water, or had been hummocked 
so as to lie above sea-level. 
Growth in Thickness. — The rate at which undisturbed ice grew depended largely 
on whether there was a heavy snow-covering or not. Hence it could come about, 
and did, that the earliest-formed ice in the winter of 1915 was not necessarily the 
thickest at the close of the year. Observations on the thickness were made at several 
different points, but ultimately these became destroyed one by one, so that by October 
there was only one small area of 1915 ice whose entire history was definitely known. 
The final measurements for thickness were made here, and gave the result that 
by October 13 ice which started forming on February 6 was now 145 cm. 
( = 4 ft. 9 in.) thick. This ice started forming in and about 77° S. lat. ; and on 
October 13 the position was 69° 20' S. lat. Owing to the abandonment of the 
ship a fortnight later, this was the last measurement possible at this locality. It is 
more than probable, however, that the ice continued to increase in thickness until 
possibly the end of December, but certainly no later than this date. On plotting 
out the different measurements and continuing the diagrammatic curve so got in 
keeping with the composite curve of past observers, an additional 3 inches can be 
assumed. The maximum thickness of one-year ice in the Weddell Sea (except fast- 
ice in high latitudes) is therefore taken as 5 feet. Anything thicker than that is 
regarded with certainty either as having been rafted at some time or other, or as 
