real currents. That, I venture to say, is still a mystery.
It almost seems as if some of the masters of aerial navigation in the
bird world were gifted with the ability to propel themselves forward by
a mere act of volition.

An interesting article on the subject of bird flight appeared not long
ago in one of the foremost periodicals of the country, a part of which
is here quoted to show what a puzzling problem we have before us:

Recent developments in aerial navigation have renewed interest in the
comparative study of the mechanical principles involved in the flying
of birds. There is one exceedingly puzzling law in regard to birds and
all flying creatures, the solution of which may work far-reaching
influences in the construction of flying craft.

"This law, which has thus far perplexed scientists, is that the heavier
and bigger the bird or insect, the less relative wing area is required
for its support. Thus the area of wing surface of a gnat is forty-nine
units of area to every one of weight. In graphic contrast to that, a
condor (_Sarcorhamphus gryphus_) which weighed 16.52 pounds had a wing
surface of 9.80 square feet. In other words, though the gnat needs
wing surface in a ratio of forty-nine square feet per pound of weight,
a great condor manages to sail along majestically with .59 of a square
foot to at least a pound of weight. The unexplained phenomenon
persists consistently throughout the whole domain of entomology and
ornithology. Going up the scale from the gnat, it is found that with
the dragon fly this ratio is 30 to 1, with the _tipula_, or
daddy-longlegs, 14.5 to 1, the cockchafer only 5.15 to 1, the
rhinoceros beetle 3.14 to 1.

"Among birds the paradoxical law that the smaller the creature the
bigger the relative supporting wings holds good. A screech owl (_Scops
zorca_) weighing one-third of a pound had 2.35 square feet of wing
surface per pound of weight. A fish hawk (_Pandion haliaetus_)
weighing nearly three pounds had a wing area of 1.08 square feet to
each pound. A turkey buzzard weighing 5.6 pounds had a little less
than one square foot of wing surface to each pound. A griffon vulture
(_Gyps fulvus_) weighing 16.52 pounds had a wing surface of only .68
square feet to the pound.

"Students of aerial navigation who are devoting much attention to
observations of birds say that if the peculiar law governing extant
flying creatures could be fathomed the problem of human flight might