THE CHALLENGER 
353 
far out of their course, so that the veil once lifted has 
dropped again, and Heard Island has drifted back into 
the unknown. 
On February 8th, 1874, the Challenger resumed her 
course southward on the meridian of 8o° E. and fared no 
better, though no worse, in the way of weather than did 
her predecessors in the same seas. The first iceberg was 
seen on the nth in 61 0 S., a beautiful flat-topped mass 
700 yards in length, floating with more than 200 feet above 
water. For some days the weather improved, and only a 
few icebergs were in sight at a time, though these were of 
exquisite beauty, especially on account of their deep azure 
colouring. It was found necessary to lay-to during the 
few hours of darkness, in order to reduce the risk of col- 
lision with floating ice, and as fogs were frequent and the 
coal supply was not so ample as to encourage the use of 
steam when sails would serve, the day’s runs were often 
very small. 
On the 15th a good deal of ice was visible, the edge of 
the pack being in sight to the southeast. A sounding was 
made in 65° 42' S., 79 0 49' E., where a depth of 1675 
fathoms was found. Temperature observations were 
made as usual at frequent intervals of depth, but the ther- 
mometers which had given excellent results in tropical 
and temperate seas now found themselves in the presence 
of conditions with which they could not cope. The deep- 
sea thermometer used by the Challenger was known as 
the Miller-Casella, a modification of the familiar Sixe’s 
form. A steel index in one limb of a tube bent into 
the shape of the letter U was left at a point indicating 
the highest temperature the thermometer had passed 
through, and a similar index in the other limb was left 
at a point indicating the lowest temperature to which the 
23 
