in any direction. But a balloon, as well as a car, is subject to severe 

 regulations. It must be constructed according to classic norms to 

 obtain its certificate of airworthiness. Now my balloon varied from 

 them in an intolerable manner, as much by the absence of a net as by 

 the extreme lightness of the construction materials (2y oz. to a square 

 yard for the upper three quarters and only ly oz. for the lower quarter, 

 the whole covered by 2y oz. of rubber to the square yard). 



An administration can make no exceptions, above all when a foreign 

 professor is in question ! The German permit was thus refused to me. 

 Fortunately the international agreements allow a Swiss aeronaut to 

 leave Germany with a Swiss certificate of airworthiness originating in 

 Berne, and Berne, more liberal, gave me the authorization asked for. 



Let us now look at the basket of our balloon, or rather at what it 

 had instead of a basket. We must have a hermetically sealed cabin, 

 carrying breathable air at ordinary pressure, and able to resist this 

 internal pressure even when the outside pressure will be no more than 

 one-tenth of an atmosphere. Our lives depend upon the airtightness 

 and the strength of this cabin. Let us, then, have a spherical cabin in 

 sheet aluminium of one-seventh of an inch (3-5 mm.) thick. The dia- 

 meter will be 7 ft. (210 cm.). Two observers, surrounded by their 

 instruments, will be perfectly comfortable here, surveying the outside 

 world through eight round portholes of a convenient diameter, that of 

 3-15 in. (8 cm.). To avoid the danger of breakage caused by the differ- 

 ence between the pressures prevailing on the two faces, these windows 

 are constructed of two sheets of glass, each 0-3 in. thick, separated by a 

 thin layer of air which contributes to thermal insulation. We thus 

 prevent the formation of rime on the windows, even in the stratosphere, 

 where the external temperature is in the neighbourhood of - 76° F. 

 These windows offer no danger of breakage even when obliged to 

 sustain a difference in pressures of nine-tenths of an atmosphere. 



I did not imagine then that, nine years later, I should construct 

 portholes to resist a pressure of 600 atmospheres. 



How could we, from this sealed cabin, manage to drop ballast 

 without air escaping ^ The principle of the air or water lock is well 

 known. Here is how, when I was still a child, I observed its functioning 

 for the first time. One day I was taken to visit a menagerie. In one of the 

 cages was a lion and a lion-tamer. How would the tamer get out with- 

 out the lion being able to follow him ? It was a revelation for the little 

 lad that I then was : the tamer went into a little adjoining cage through 



[<5] 



