THE BONES. 
41 
perfected by studying the mode by which the great 
Creator accomplishes His purposes. 
It is evident, that a creature thus furnished with 
bones so much lighter than those of other animals, 
must have a prodigious advantage in raising itself 
in the air. But besides this superior lightness of 
the skeleton, these bones, from their hollow struc- 
ture, act as pipes, supplying air in abundance ; and 
thus not only rendering the bird still lighter, but 
enabling it to breathe at heights, at which a human 
being would be gasping for breath. Travellers who 
have ascended very high mountains, find that when 
they get near the summits, the air becomes so 
rarefied and thin, that it is as much as they can do 
to proceed at a slow pace. Those birds, too, whose 
habits never lead them into the more elevated 
regions of the atmosphere, and are therefore, not 
so abundantly provided with additional capacities 
for retaining air, have been observed to suffer 
severely, as was proved by a Mr. Robertson, who 
took two birds up with him in a balloon, one of 
which actually died at the height of 15,600 feet; 
whereas, others better provided with air-cells appear 
to feel no such inconvenience. 
Mont Blanc, the most elevated mountain in 
Europe, is not quite three miles high ; and yet on the 
top, breathing is extremely difficult ; nevertheless, 
the Condor of South America, the largest bird gifted 
with the power of flight, will dart upwards suddenly 
from the deepest valleys to a considerable height 
above the summit of even the lofty mountain of 
Chimborac^o, which is one fourth part higher than 
Mont Blanc. Humboldt, the celebrated traveller, 
