THE BEAUTIFUL LADDER. 
229 
all that is perceptible.” There is another fact 
mentioned by those who have watched their 
movements most closely, which corresponds 
with the explanation already given—namely, 
the fact that the axis of the humming-bird’s 
body when hovering is always highly inclined — 
so much so as to appear almost perpendicular 
in the air. In other words, the wing-stroke, 
instead of being delivered perpendicularly down¬ 
ward, which would infallibly carry the body on¬ 
ward, is delivered at such an angle forward as 
to bring to an exact balance the upward, the 
downward, and the forward forces which bear 
upon the body of the bird. Mr. Darwin says: 
“ When hovering by a flower, the tail is con¬ 
stantly shut and expanded like a fan, the body 
being kept in nearly a vertical positionP Mr. 
Wallace, another accurate observer, describes 
the humming-birds as balancing themselves 
vertically in the air.” ’ 
“To the exact accuracy of these statements 
can be added the testimony of many years of 
close observation; and not the least wonder of 
the whole operation is that the bird is able at 
all to use the wing-muscles with such lightning 
rapidity—so rapid as to give the peculiar bullet- 
20 
