Page:Scott's Last Expedition, Volume 1.djvu/382

248 temperature and pressure is attached beneath a small flag and hung 10 to 15 ft. below the balloon with balloon silk thread; this silk thread is of such fine quality that 5 miles of it only weighs 4 ozs., whilst its breaking strain is 1¼ lbs. The lower part of the instrument is again attached to the silk thread, which is cunningly wound on coned bobbins from which the balloon unwinds it without hitch or friction as it ascends.

In order to spare the silk any jerk as the balloon is released two pieces of string united with a slow match carry the strain between the instrument and the balloon until the slow match is consumed.

The balloon takes about a quarter of an hour to inflate; the slow match is then lit, and the balloon released; with a weight of 8 ozs. and a lifting power of 2½ lbs. it rises rapidly. After it is lost to ordinary vision it can be followed with glasses as mile after mile of thread runs out. Theoretically, if strain is put on the silk thread it should break between the instrument and the balloon, leaving the former free to drop, when the thread can be followed up and the instrument with its record recovered.

To-day this was tried with a dummy instrument, but the thread broke close to the bobbins. In the afternoon a double thread was tried, and this acted successfully.

To-day I allotted the ponies for exercise. Bowers, Cherry-Garrard, Hooper, Clissold, P.O. Evans, and Crean take animals, besides Anton and Oates. I have had to warn people that they will not necessarily lead the ponies which they now tend.

Wilson is very busy making sketches.