this scientific object. These were my first trips. I had in the interior of 

 the balloon, along its vertical axis and also in the neighbourhood of its 

 equator, a dozen electric thermometers, thermo-couples whose cold 

 junctions were in the basket of the balloon. I myself constructed a 

 simple and exact potentiometer and by means of an Einthoven galvano- 

 meter I could measure the temperatures of the gas within approxi- 

 mately a tenth of a degree. At the same time I could, by means of a 

 rubber tube, take samples of gas from different parts of the balloon when 

 it was at different heights and from them determine the density by means 

 of a bunsen apparatus. This permitted me to follow the diffusion of the 

 air coming in through the neck and being slowly mixed with the gas. 

 All these measurements were made for daytime and for night-time at diff- 

 erent altitudes, so as to show more clearly the influence of solar radiation. 



These studies familiarized me with the balloon. I did not then think 

 that later they would lead me into the stratosphere. 



I have said that it was the study of cosmic rays which had led me into 

 the stratosphere. As a matter of fact I had also another reason for going 

 up there myself: I wanted to induce the air services to use the high 

 atmosphere, to travel at high speeds at an altitude where the rarefied 

 air offers less resistance. But since, in the stratosphere, the low pressures 

 make human life impossible, I was going to have to make use of an 

 airtight cabin permitting the maintenance of an almost normal atmos- 

 phere. The specialists of those days considered my suggestion as 

 unrealizable. What today appears elementary to us, in those days 

 seemed Utopian. But the single objection that they were able to make 

 to me was that up till then no one had ever done it. How often have I 

 heard reasoning of this sort! But it is just the function of the engineer 

 to place his reliance upon theory when creating something new. If I 

 had been an aviator I should perhaps have constructed, at the begin- 

 ning, a stratospheric aeroplane. But being an aeronaut I plunged into 

 the construction of a balloon. It was besides a relatively simple thing 

 to suspend an airtight cabin to the free balloon. 



The Belgian National Fund for Scientific Research {Fonds National 

 Beige de la Recherche Scientifique)^ which had just been founded by 

 King Albert I, supported my project and accorded me the necessary 

 credits. In homage to the Fonds National the balloon was baptized the 

 FNRS. 



I wanted to ascend, as I have said, to meet the cosmic rays at a point 

 where they would not yet have traversed more than a tenth of the 



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