A night watchman has been instituted mainly for the purpose of observing the aurora, of which the displays have been feeble so far. The observer is to look round every hour or oftener if there is aught to be seen. He is allowed cocoa and sardines with bread and butter – the cocoa can be made over an acetylene Bunsen burner, part of Simpson’s outfit. I took the first turn last night; the remainder of the afterguard follow in rotation. The long night hours give time to finish up a number of small tasks – the hut remains quite warm though the fires are out.
Simpson has been practising with balloons during our absence. This morning he sent one up for trial. The balloon is of silk and has a capacity of 1 cubic metre. It is filled with hydrogen gas, which is made in a special generator. The generation is a simple process. A vessel filled with water has an inverted vessel within it; a pipe is led to the balloon from the latter and a tube of india-rubber is attached which contains calcium hydrate. By tipping the tube the amount of calcium hydrate required can be poured into the generator. As the gas is made it passes into the balloon or is collected in the inner vessel, which acts as a bell jar if the stop cock to the balloon is closed.
The arrangements for utilising the balloon are very pretty.
An instrument weighing only 2 1/4 oz. and recording the 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 1 1/4 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 oz. and a lifting power of 2 1/2 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.