ROTCH. — EXPLORATION OF UPPER AIR. 249 



above the earth, where the pressure is about one ninth that at the earth, 

 the balloon must lift itself from the ground when one ninth filled with 

 gas. Therefore a relatively large balloon is required, and its initial 

 velocity of ascent is great, because it is found advantageous to fill the 

 gas-bag completely. The greatest difficulty has been to protect the ther- 

 mometers from insolation, and to insure records being made, notwith- 

 standing the great cold to which the instruments are exposed. 



The first systematic experiments of the kind were made in Paris, in 

 1893, by G. Hermite, who was later associated with G. Besan^on. 

 There have been six high ascents from Paris of the three balloons 

 called V Acrophile. The second one of the name had an envelope of 

 gold-beaters' skin, with a capacity of 6,3G0 cubic feet, which when nearly 

 filled with coal-gas gave an initial lifting power of 235 pounds, in ex- 

 cess of its own weight of 49 pounds, and the instruments and screens, 

 which weighed 12 pounds. With this balloon, in October, 1895, at an 

 approximate height of 46,000 feet, a temperature of — 94° Fahrenheit 

 was recorded, which is the lowest noted in a balloon, and probably the 

 lowest natural temperature observed on the earth. The average decrease 

 of temperature was 1° Fahrenheit for 320 feet of height. The instru- 

 ments used are of the well known Richard type, and have been tested in 

 a chamber whose pressure and temperature are lowered to the limits 

 which it is expected may be reached by the balloon. They are placed 

 below the balloon in a wicker tube six feet high, lined with silvered paper 

 to ward ofi the sun's rays. It is believed by Hermite, that during the 

 rapid ascent of the balloon the draught of air through the tube is suffi- 

 cient to neutralize the heating of the enclosed air by the sun. It is 

 admitted that when equilibrium is nearly reached this may not be true, 

 and that the temperature recorded near the highest point may be too 

 high. To avoid freezing of the ink the registration is now made on 

 smoked paper, and to protect the instrument from shocks it is hung by 

 springs in a closed basket, which is itself suspended in the tube already 

 mentioned. An apparatus for obtaining samples of air at high altitudes 

 has been carried by the balloon, but as yet without success, owing to 

 difficulties in hermetically closing the receiver after the air has entered, 

 since mechanically closing the inlet tube and sealing it by heat generated 

 chemically have each proved ineffectual at great heights. 



By means of a grant from the German Emperor to the Deutsche 

 Verein zur Forderung der Luftschiffahrt, R. Assmann, A. Berson, and 

 others in Berlin, have been able to carry on an extensive series of mete- 

 orological investigations with manned balloons, and also with a captive 



