ALTITUDE OF THE MIGRATION FLIGHT 61 



for active exertion ; and for a bird starting for a long flight at a 

 great elevation, it seems especially imjierative that its weight 

 should be as small as possible. The balloon expedition referred to 

 above did not start till noon, and the pigeons which were taken up 

 would therefore undoubtedly have their crops well filled; they 

 would accordingly be so little adapted for the experiment they had 

 to undergo that it is surprising that, in the case of most of them, 

 the results were so favourable. 



On the other hand, the various mountain ascents undertaken, 

 since Humboldt's Chimborazo expedition, sufficiently demonstrated 

 how little man — and unquestionably all other warm-blooded 

 creatures — are capable of approaching even to the summits of the 

 highest elevations of the earth's surface by the sole use of their 

 corporeal powers. At heights of from 20,000 to 22,000 feet, the 

 difficulties of breathing and the general exhaustion are such as to 

 render even the least corporeal efforts impossible. Gay Lussac, on 

 Chimborazo, was able to remain only a quarter of an hour at a 

 height of about 20,000 feet. The brothers Schlagintweit succeeded, 

 at Ibi Gamin, in reaching an elevation of 22,259 English feet, but 

 became so completely exhausted as to be obliged to give up all 

 further attempts to proceed higher. The men accompanying them 

 were also utterly exhausted. 



During balloon voyages for scientific ends, with the body kept 

 in a perfect state of rest, it has undoubtedly been possible to reach 

 con.siderably greater elevations; but in all such cases the inves- 

 tigators invariably did so at the risk of their lives. Thus Tissandier, 

 Spinelli, and Siwel fell unconscious on attaining a height of 26,000 

 feet ; the last two, in fact, never recovered consciousness. Glaisher 

 reached a height of 29,000 feet before losing consciousness; his 

 companion, Coxwell, on the other hand, though completely stiff 

 with cold was yet able, while the balloon was continuing to 

 asceiid, to grasp the cord of the valve with his teeth, and by 

 opening it cause the balloon to descend, without having lost 

 consciousness. 



The sum of our experiences accordingly proves that neither man 

 nor any other warm-blooded creature is, while making corporeal 

 exertions, capable of ascending to heights much above 22,000 feet ; 

 and that, in the case of man, the ascent to elevations beyond 26,000 

 feet is, even when the body is kept in a perfectly quiescent state, 

 attended by the utmost risk of life ; whereas birds, on the other 

 hand, can, of their own complete free will, elevate themselves to 

 heights of from 3.5,000 to 40,000 feet, and can at such heights 

 sustain great muscular efforts for any desirable length of time 

 without being affected either by the great rarity of the air, or its 



