Title I 

 DIMINISHED PRESSURE 



Preliminary Chapter 

 THE LOFTY REGIONS OF THE EARTH 



The effects produced upon the organism by a great and sudden 

 decrease in the barometric pressure can be observed in three dif- 

 ferent cases: mountain journeys, balloon ascensions, and experi- 

 ments under pneumatic bells. 



These last two methods were absolutely unknown to the an- 

 cients. Galileo, as everyone knows, was the first to have a clear 

 idea of the pressure of the air; it was not until 1640 that Toricelli 

 invented the barometer, or until 1650 that Otto de Guericke in- 

 vented the pneumatic machine. In 1648, at the suggestion of our 

 great Pascal, Perier made at Puy-de-D6me the memorable experi- 

 ment in which he saw the height of the barometric column de- 

 crease in proportion to the increase of the altitude of the place 

 where it was observed. 



For balloons, the discovery is still more recent. The first hot air 

 balloon which carried aloft Pilatre du Rozier and the Marquis 

 d'Arlandes, ascended from Paris November 22, 1783; a few days 

 after, December 1, Charles made an ascension with the hydrogen 

 balloon which he had just invented. This balloon, however, was 

 not able to carry the observers high enough for the decrease of 

 pressure to make its effect felt upon them. In fact, the experiment 

 proved that this effect is not clearly evident in a balloon below an 

 altitude of 5,000 or 6,000 meters. Consequently, among the thou- 

 sands of ascents which followed that of Charles and Robert, only 

 a very small number can be of interest to us in our particular 

 purpose and therefore be reported in this historical review. 



