1921.] Lhe Highth Indian Science Congress. cix 
carrying instruments which are made very light indeed. Fi 
12 shows such a balloon six feet in diameter, partly filled with 
hydrogen and ready to be sent up with its recording instru- 
ment. The weight of a six-foot balloon of this material is 
about 250 grms. (3 Ib.) and when it has filled itself out com- 
pletely by the expansion during the ascent of its partial charge 
of hydrogen it has a free lift of about 3,000 grms. (63 Ib.) 
which is gradually lost by efflux of gas on further expansion as 
the balloon rises, until at some 18 km. (11 miles) height the. 
balloon, with its load, floats in equilibrium, and is thereafter 
brought down by leakage or some automatic means of rup- 
turing it. 
30. Instruments of a sufficiently light type to comply 
| 
Fie. 12. 
humidity throughout the range of height traversed by the 
balloon. At the time when we in India began to pay attention 
to this method of experiment, Mr. Dines’ instruments were not 
available for purchase and in making our own we adopted the 
ingenious principle of his recorder, at the same time trying 
still further to reduce the weight and so to diminish the cost 
of reaching a given h 
eight. : : 
The result is shown in Fig. 13b and the instruments 1s on 
