Airships past and present, together with chapters on the use of balloons in connection with meteorology, photography and the carrier pigeon . to the ground. Experience shows that a free kite-balloonmaintains its position with very little change, if held by arope attached to the front, though in this case it is generallyinclined at a greater angle to the horizontal. CHAPTER XVII. Instruments. The most important instrument is the barometer, which isused for determining the altitude. The balloonist must knowthe height to which he has risen, and also notice any tendencyto rise or fall as soon as p
Airships past and present, together with chapters on the use of balloons in connection with meteorology, photography and the carrier pigeon . to the ground. Experience shows that a free kite-balloonmaintains its position with very little change, if held by arope attached to the front, though in this case it is generallyinclined at a greater angle to the horizontal. CHAPTER XVII. Instruments. The most important instrument is the barometer, which isused for determining the altitude. The balloonist must knowthe height to which he has risen, and also notice any tendencyto rise or fall as soon as possible. There is a certain sluggish-ness about aneroids, which can be corrected by gentle method, which has been described, of throwing out pieces of paper or feathers forms auseful indication of a rise orfall, and may conveniently sup-plement the use of the baro-meter. On an ascent in a free balloon,a barograph is always taken,which records the barometricreading on a roll of paper, andtherefore, together with thenotebook, forms a concisestatement of the facts of thejourney. The statoscope hasalso been described, and is by. Fig. 118.—Aneroid barometer. no means indispensable, but a compass must be taken in any meteorological observations, a wet and dry bulb thermo-meter, preferably of the Assmann type, should be taken, inorder to measure the temperature and the moisture in theatmosphere. Eadiation is, however, more important than actualtemperature. The gas inside the balloon is warmer than thesurrounding atmosphere, except by night, when the temperaturesof the two are nearly the same, the gas being sometimes slightlythe colder of the two, owing to losses by radiation. It is very necessary to take good maps of the district. But on INSTRUMENTS. 193 a long journey, they are apt to be so numerous that they are nowoften replaced by maps on a very small scale, which are readby means of a magnifying glass. As this system is possibly amatter of some general inte
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