THE DRIFT. 285 
with the thermometer at —24°, to find, if I could, the 
cause of a sound a good deal like that of the surf, I 
was startled hy a noise like a quarry blast, explosive 
and momentary, followed by a clatter like broken glass. 
Some ten minutes afterward, it was repeated, and a 
dark smoke-like vapor rose up in the moonlight from 
the same quarter. These things keep us on the qui 
vive. 
January 16. In the course of a tramp to-day about 
noon, the thermometer standing at —18°, I came across 
a wonderful instance of the yielding elasticity of ice 
under intense pressure. About two hundred yards 
from the brig, on her starboard quarter, was an un- 
broken plain of level ice, which before our recent break- 
up used to form one of my daily walks. It measured 
one hundred and thirty paces in its longer diameter 
and eighty-five in its shorter, and its thickness I ascer- 
tained this morning was over five feet. I found in 
crossing it to-day that the surface presented a uniform 
curve, a segment whose versed sine could not have 
been less than eight 'feet, abutted on each side by a 
barricade of rubbish. It strikes me that the dehis- 
cence, lady's slipper or Rupert's drop fashion, of such 
tensely-compressed floes, must be the cause of the loud 
explosions we have heard lately. At —80° or —40° 
the ice is as friable and brittle as glass itself ; besides, 
one of those yesterday was followed by a ringing 
clatter. 
January 18. The extreme stillness, and the facil- 
ity with which sound travels over these Polar ice- 
plains, make us err a good deal in our estimates of dis- 
tance at night. I went out to-day with Dr. Vreeland 
in search of a violent disruption of the ice, which our 
look-outs declared they had heard at the very side of 
t 
