A WHEWELLITE ESSAY ON MARS. 143 



The experiment has never yet been tried. Nor is it 

 easy to see how it could be. Aeronauts have reached 

 a height where the atmospheric pressure has been 

 reduced to below seven inches of the common baro- 

 meter ; but in attaining this height they were ex- 

 posed to other effects than those due to the mere 

 tenuity of the atmosphere. I refer here to the cele- 

 brated ascent by Coxwell and Grlaisher, on July 17, 

 1862, when the enormous elevation of 37,000 feet was 

 attained, or nearly two miles above the summit of the 

 loftiest mountain of the earth. But, although the cir- 

 cumstances of such an ascent do not altogether cor- 

 respond to those depending solely on atmospheric rarity, 

 it is probable that the most remarkable effects result 

 from this cause, and therefore it will be well to consider 

 what happened to the aeronauts on this journey. 

 'Previous to the start,' says Flammarion, in a work 

 edited by Mr. Grlaisher, ' Grlaisher's pulse stood at 76 

 beats a minute ; Mr. Coxwell's at 74. At 17,000 feet, 

 the pulse of the former was at 84 ; of the latter at 100. 

 At 19,000 feet, Grlaisher's hands and lips were quite 

 blue, but not his face.' At this height the atmospheric 

 pressure was reduced to about one-half the pressure at 

 the sea-level ; in other words, the pressure corresponded 

 to about fourteen and a half inches of the mercurial baro- 

 meter. After passing beyond this height, distressing 

 symptoms were experienced by both aeronauts. ' At 

 21,000 feet, Grlaisher heard his heart beating, and his 

 breathing was becoming oppressed ; at 29,000 feet he 

 became senseless, and only returned to himself when 



