of age, the rubberized envelope began to split and the balloon was 

 unusable as a gas aerostat, Cosyns and I tried to make a Montgolfier 

 (hot-air balloon) out of it. The attempt was not devoid of interest : 

 moving with the air, the spherical balloon would have escaped the 

 cooling action of the wind, and the heat of the sun would have warmed 

 it sufficiently to keep it in equilibrium without auxiliary heating. 

 However, the neck was too small for a hot-air balloon : driven back by 

 a sudden wind before the take-off, the envelope took fire and was 

 destroyed in a few seconds by the flames. 



The advent of electronic instruments might have sounded the knell 

 of the era of the stratospheric balloon : in fact, equipped with auto- 

 matic instruments, sounding-balloons today allow us to make meteoro- 

 logical and physical observations in better conditions and at less cost. 



But the aerostat still has a task to fulfil: that of observing the 

 spectrum of solar light reflected by the planets. If we can attain this, 

 we shall know the composition of the atmosphere which surrounds 

 these celestial bodies. We shall know then if there is oxygen in the 

 atmosphere of the planet Mars, hence if, from this point of view, life 

 is possible there. For that, a spectrograph must be directed upon Mars ; 

 but no mechanical device as yet allows us to direct a telescope auto- 

 matically upon a heavenly body : the presence of an observer is indis- 

 pensable. So that terrestrial oxygen may not falsify observations the 

 astrophysicist should not have above him more than one-hundredth 

 of the terrestrial atmospheric layer : or in other words, he should rise 

 to over 1 8-2" miles. At that height the lifting force of a metric cube 

 of hydrogen (33-9 cu. ft.) is reduced to 10 grams (y ounce): the 

 balloon would have to be, at once, extra-light and of large volume. 

 My brother's Pléiade^ with its hundred rubber ballonets which sup- 

 port the cabin, would seem to be of particular interest : during a pre- 

 liminary trial it attained the altitude aimed at of 9900 ft. 



Nevertheless, to reach over 1 8^ miles of altitude it would be neces- 

 sary to increase the volume and the number of ballonets of the Pléiade 

 and, naturally, make use of an airtight cabin. The cost of such an 

 experiment would rise in proportion: for the moment it cannot be 

 attempted, money lacking: it is a pity. My friend Audouin Dollfus, 

 astronomer and aeronaut, is making efforts at the present time towards 

 this end. I hope he will bring them to a satisfactory conclusion. 



After having journeyed through the stratosphere, let us now 

 penetrate the oceanic deeps. 



[ 18 ] 



