3i8 THE POPULAR SCIENCE MONTHLY. 



earth, many a bold aeronaut has gone above the clouds. Only after 

 they have reached the height of 6,000 metres do they usually expe- 

 rience symptoms resembling those of mountain-sickness. 



But on land these symptoms make their appearance at elevations 

 far lower, and differing according to locality. In the Alps, definite 

 symptoms first appear at 3,000 metres; in the Bolivian and Peruvian 

 Andes, at 4,000 metres ; higher still, in the equatorial Cordillera and 

 on the Himalaya. In general, the elevation at which they first appear 

 depends upon that of the line of everlasting snow, the lower limit of 

 mountain-sickness being situated a little above the snow-line. The 

 influence of the temperature is very evident. As for anomalies spe- 

 cial to circumscribed localities or to individuals, the consideration of 

 them would take us beyond the bounds we have set for ourselves here. 



These grave and curious symptoms have been explained in many 

 different ways by travelers, physicians, and experimenters. As for 

 the native mountaineers, they solve the problem of their origin by 

 referring them either to supernatural intervention or to the influence 

 of noxious efliuvia. In the Ancles these efiluvia are reputed to be 

 of an antimonial nature ; in the Himalaya the cause is supposed to 

 be vegetal poisons given forth from flowers, mosses, etc. These hy- 

 potheses need not detain us. 



Among the many theories more or less tenable a priori^ but none 

 of which will stand the test of experiment, there is one which is al- 

 most universally accepted, and which reckons De Saussure among its 

 distinguished supporters. It is known that the atmospheric pressure 

 on a square centimetre of surface is 1.03 kilogramme. If we multiply 

 this by the number of square centimetres of surface in a man's body, 

 the product is something enormous. Take an average case, a pressure 

 of say 15,000 kilogrammes. We are in equilibrium with this great 

 pressure, they say ; lessen the pressure, and the result is like the ap- 

 plication of an immense cupping-glass over the entire surface of the 

 body. The heart's action is now no longer sufficiently counterbal- 

 anced, and hence congestion and hseraoi-rhage of the mucous mem- 

 branes and of the skin, engorgement of the blood-vessels of the face, 

 cerebral troubles, and the rest. 



It is amazing to find a theory so plainly at variance with element- 

 ary physical laws accepted by eminent men. What would be the 

 result if we had to bear upon the surface of the body a pressure of 

 15,000 kilogrammes, and if every variation of the barometer added 

 or subtracted from this sum one or two hundred kilogrammes ? 



Another theory, first offered by De Saussure, is far more worthy 

 of attention. " On the top of Mont Blanc (4,810 metres)," says he, " the 

 air is nearly one-half less heavy than at the sea-level ; hence it results 

 that if, in a given time, we pass through our lungs a given volume of 

 air, that volume will represent only about one-half the weight of the 

 same volume of the air to which we are accustomed. Hence there 



