January 26, 1894. 
tion. If at any point of its course the bird readjusts his 
position so as to present the full area of his wings to the 
line of flight, he will shoot upward, still with motionless 
wings, to a height of some feet, but never to the height 
from which he descended. I have seen aneagle at the end 
of a half-mile sail, glide upward ten or fifteen feet to his 
objective point, and I think this is about the limit he can 
altain without beating his wings. 
Now with the aerodrome of Professor Langley’s dream, 
if, with an initial impulse, it could be maintained on a 
horizontal, forward, course by adjustments of its inclina- 
tions to the internal working of the column of air over 
which it is passing, its force of gravity would be immedi- 
ately neutralized, and its onward flight consequently 
arrested. A plane body many times heavier than air can- 
not be sustained in direct horizontal flight through the 
air, except by an expenditure of internal energy sufficient 
to propel it with a speed proportionate to the require- 
ments of its specific gravity, qualified by its surface area. 
Professor Langley will not have failed to observe, or 
the mention of the fact will recall it to his recollection, 
that sailing-birds pursuing an onward course do not main- 
tain a horizontal line by availing themselves of any inter- 
nal motion in the air, but simply by their own unaided 
physical energies. 
Recurring now to the less clearly apprehended problem 
of circling, I believe that Professor Langley’s argument 
that the bird could not circle with motionless wings in a 
horizontal current, requires one important qualification— 
he should have added ‘‘at least not if he carries his own 
wings level with the horizon.” This the circling bird 
never does. He could no more circle while he did so, 
than a bicyclist could circle on an upright wheel. But by 
holding his wings obliquely to the horizontal circle of his 
flight, he can utilize the wind as a lifting power for about 
five-eighths of his course,and for propulsion also over nearly 
the same length, provided the wind blows faster than he flies. 
This is precisely on the principle on which a perforated card 
or messenger screws its course up the string ofakite. The 
wind blows horizontally but strikes the messenger obliquely. 
If the bird describes an oval, facing the wind only on the 
short course, he may utilize the wind for driving, over 
three-fourths of the course or even more. There is hence 
at every sweep an accumulation of impulse to urge it over 
the difficulty of sailing against the wind. At that stage, 
the bird can most easily adjust his wings, so as to make 
the opposing air lift him ; the effort is required only to 
force himself into the wind’s eye. By gliding slightly 
downward over the one-half or more of the course, with 
the wind, he acquires an impulse from the joint action of 
wind and gravity, almost, or quite sufficient, to drive him 
over the remainder of the course, and to raise him to his 
original level while facing the wind. If the impulse is not 
strong enough, the effect will be seen, not necessarily in the 
bird falling to a lower level, but in his circling further and 
further to leeward at every sweep. In fact the aero- 
drome of the future, although, like the bird, it may not sail 
a straight horizontal course without an expenditure of 
energy, may nevertheless, like the bird, be maintained in 
circling flight, in a moderate breeze, indefinitely, with a 
minimal expenditure of energy, not in consequence of the 
“internal work” of the air, but in spite of-it. But while 
this explanation of the mechanics of circling flight renders 
it conceivable that, given the initial impulse, it can be ac- 
complished in a moderate breeze without any expenditure 
of energy, beyond what is required for constant readjust- 
ment of the inclination of the plane, I am by no means 
certain that, in the case of the bird, the tail is not an im- 
portant adjunct in propulsion. ‘This obliquity of the direc- 
tion of the wings to the horizon of flight is the clue to the | 
whole mystery of circling or soaring flight. 
Sele NCE: 
47 
The clue being given, the following propositions will, I 
think, serve to completely unravel it : 
First. A bird gliding down an inclined plane owes his 
forward flight to the force of gravity. 
Second. To maintain himself in horizontal flight, 
whether in a direct line or in a circle, power is necessary, 
first to overcome the force of gravity, second to propel 
him on his course. 
Third. The bird flying in a direct line provides both 
lifting and driving power by beating his wings, as the boat- 
man uses his oars ; the circling bird achieves the same 
ends by trimming his wings to the wind, as the sailor trims 
his sails. Professor Langley suggested the solution when 
he argued that the power must come from the air. 
LETTERS TO THE EDITOR. 
_ #* Correspondents are requested to be as brief as possible. The writer’s name is 
in all cases required as a proof of good faith. 
On request in advance, one hundred copies of the number containing his communi- 
cation will be furnished free to any correspondent. 
: eeere diten will be glad to publish any queries consonant with the character of the 
journal. 
A Curiosity in the Vegetable World. 
Near acountry roadside in Tate County, Miss., is a 
curiosity which is of interest to every passer-by, but is 
especially interesting to a student of nature. 
All of us, doubtless, have observed ‘‘ twin” or 
“double ” trees, which have a common stock for some 
distance above ground, and which might be accounted 
for by the cessation of growth of the terminal bud of 
the trunk, and by the upward development of two 
branches from lateral buds. But the phenomenon I 
speak of is this : two large elm trees (Ulmus Americana) 
about 1/2 and 2 feet in diameter, respectively, have 
crossed each other, and have grown together, in this 
wise. ‘The trees are about 8 feet apart at the base, and 
one crosses the other about 6 feet from the ground, 
the trees and the ground between forming a right-angled 
triangle ; rather an obtuse-angled triangle ; for the tree 
which is most nearly erect is inclined slightly in the 
direction in which the other lies. It seems that when 
young, or at least some years ago, one of the trees was 
blown up against the other, the two uniting where they 
crossed as solidly as if one were a branch of the other, the 
one growing almost upright, while the other continued its 
growth in a nearly horizontal direction. 
The latter is, I should say, about 50 feet long, and the 
upper end of its trunk about 15 feet from the ground. 
T. O. Masry. 
” 
University of Mississippi, Jan. 23, 1894. 
Red Ants. 
A sHorT time since I read an article in Sczence con- 
cerning red ants. I wish someéody could tell me how to 
rid a building of them. 
Upon our grounds are two buildings, hardly fifty rods 
apart, the ‘‘South Hall” being infested from garret to 
cellar and the ‘‘ North Hall” being absolutely free from 
them. I can find no great difference of soil or position 
to account for this. Why the one building should be so 
infested with them and the other zof is more than I can 
explain. I have tried almost every known remedy 
against them without success. 
For weeks, even months, our rooms will be appa- 
rently clean and free from these pests. Let me bring 
a piece of meat on a plate into the room, set it any- 
where I choose, and within twenty-four hours there 
will be hundreds,—if it remain over night thousands,— 
literally, of them covering it and the neighboring ob- 
