820 
MR J. M. WORDIE ON THE NATURAL HISTORY OF PACK-ICE 
measurements of ablation went, the results round the ship were nil. These 
measurements took the form of a marked stake embedded in the ice of some 
prominent hummock. One such was set up on May 21, 1915, and when examined 
for the last time on September 4, as on previous visits, it was found still crusted, 
like the ice around, by rime 1 inch thick. This was the rule everywhere through- 
out the winter. 
In the summer, conditions were not quite the same, and changes did occur, but 
they were directly the outcome of the sun’s heat. This was the very season during 
which quantitative measurements would have been of most value ; but such were 
of course quite impossible after the ship was crushed in October 1915. The 
summer changes are therefore the result 
of comparative observation, and quanti- 
tative tests are still required. 
That the change from fibrous ice ( i.e . 
striated ice showing vertical lines) to 
spotted ice can take place in hummocks is 
not new ; the details of what takes place 
have been set down very clearly by Ham- 
berg. They amount to this : that the 
ice, when subjected to a temperature at 
and about the melting-point, loses some 
of the liquid salt inclusions, their place 
being taken apparently by air-bubbles ; 
the ice then ceases to show its pro- 
nouncedly striated or fibrous appearance 
and becomes bubbly and almost granular. 
Traces, however, of the vertical lines can still be seen on very close examination 
and are a convincing proof of what has taken place. What had not been settled 
by Hamberg was the length of time necessary to effect this change. The length 
of life of the Weddell Sea floes being known, it can be definitely asserted now 
that the change can be effected in one summer. 
One can also go further than this and say that the change may also commence 
while the floe is still in the water. In this connection the thick floes examined 
on August 8, 1915, and March 19, 1916, were of considerable value for what 
they told. 
That examined on August 8, 1915, which is roughly sketched in fig. 8, was 
raised up into a pressure hummock on August 1 ; previously it formed part 
of an old floe which had lain ahead of the ship since very early in February 1915, 
and which was formed at that time by the cementing together of brash and ice 
pieces (dating from 1914) during the north-east blizzards of the latter part of 
January 1915. The upper portion, just over 80 cm. in thickness, was spotted 
