44 Influence of Atmospheric Pressure 



He conjectures that this sensation may depend on the mecha- 

 nism of the joints and equipoise of the bones being disturbed 

 by the low atmospheric pressure ; and the experiments of the 

 two Webers, recently made at his suggestion, have afforded a 

 singular confirmation of this idea.* 



The observations in ascent by balloons, now become so fa- 

 miliar to us, shew, even unexpectedly in degree, the extent 

 to which the body can undergo the most sudden changes of at- 

 mospheric weight, without any very obvious effect, where the 

 health is unimpaired, and no causes of bodily fatigue are con- 

 joined. In the note below, I have stated some facts derived 

 from the best authority we now possess on this curious subject, t 



* Po^endoriPs Annalen fiir 1837, No. I. These experiments, made upon 

 the hip-joint after the tAvo bones had been detached by cutting the capsular 

 membrane through, shew that the pressure of the air will still retain the 

 head of the thigh-bone firmly in the socket, from which it sinks down when 

 the air is artificially rarefied underneath ; the joint thus becoming a sort of 

 air-pump, in which the head of the thigh-bone acts as a piston. [We pub- 

 lished an account of the above-mentioned very curious experiments, by Pro- 

 fessor Wilhelm Weber, in vol. xxv. of this Journal, p. 254. We would also 

 refer our readers to M. Boussingault's account of the effects of the air of high 

 elevations on the human frame, published in this Journal, vol. xix. p. 98. — 

 Edit.] 



t I have been recently favoured with these observations by Mr Green, 

 whose boldness and ability as an aeronaut have given him such general and 

 well-merited reputation. Having now ascended in balloons with more than 

 400 persons, under every possible variation of height, rapidity, and state of 

 atmosphere at the time, his evidence on the points in question is far more 

 complete than any other we possess. 



IVIr Green informs me that he has found none of these individuals sensibly 

 affected, otherwise than by the sudden change of temperatiire and by a noise 

 in the ears, compared by some to very distant thunder ; the latter sensation 

 occurring only during rapid ascent or descent of the balloon, and, when great- 

 est in degree, far less distressing than that produced by descent in a diving 

 bell. He has never felt his own respiration hurried or oppressed, except 

 when exerting himself in- throwing out ballast, or other management of the 

 balloon, or when suddenly passing into a very cold atmosphere. His pulse 

 is occasionally quickened ten or fifteen beats, but this only when some such 

 exertion has been sustained. He mentions to me expressly, that in no in- 

 stance have his companions experienced vertigo or sickness ; thus rendering 

 doubtful one of the statements current on this subject, and shewing how little 

 the two great functions of circulation and respiration are disturbed, under 

 circumstances where much effect might have been anticipated. 



Though the inference is limited to two persons, yet it may be worth while 

 to mention the great experiment made by Mr Green and Mr Rush in Sep- 

 tember 1838, in ascending to the height of 27,136 feet, or b\ miles above the 

 level of the sea ; the greatest elevation ever reached by man, and very exactly 

 correspondingwith the highest ascertained summit of the Himalaya mountains. 



