40 
THE BONES. 
The hones of birds, like those of animals, are for 
the most part white, hut in other respects they 
differ materially from those of four-footed animals, 
being composed of a thin, firm, and partly elastic 
substance, formed in layers, apparently fastened 
together, and almost always hollow; the cavities 
never containing marrow, but air, and communi- 
cating with the lungs, by considerable openings ; 
whereby they are rendered buoyant and light, to a 
much greater degree than is generally supposed. 
Thus a portion of the leg of a goose, about two inches 
in length, weighed about forty grains, while a piece 
of the leg of a rabbit (the marrow having been ex- 
tracted, and both being perfectly dry, and as nearly as 
possible of the same thickness and length,) weighed 
seventy-five grains, or nearly twice the weight of 
the similarly-sized bone of the goose; and yet so 
firm and strong was this latter, that, although in 
diameter it was less than one-eighth of an inch, and 
the solid tubular part not more than one-hundredth 
part of an inch in thickness, it could not be broken 
asunder by the hand. 
It is upon this principle mechanics and engineers 
act in constructing strong supports, knowing that if 
any quantity of material is to be fabricated into a 
rod of a certain length, the rod will be strong in 
proportion to its thickness ; and that if the figure 
remains the same, that thickness can only be in- 
creased by making it hollow. Therefore, hollow 
rods or tubes of the same length and quantity of 
matter have more strength than solid ones of less 
diameter. This is but one out of the hundreds of 
instances, in which the wisdom of man has been 
