« PreviousContinue »
mechanism of the flight by sailing and in particular this paradoxical fact that the bird can rise and make headway against the wind.
Many explanations have been proposed, some fantastic, others the discussion of which leads to such absurd deductions as the realization of perpetual motion; others again, true perhaps in certain particular cases, could not be embraced in a general theory. To this last class belong the hypotheses based on the utilization of the ascendant currents and on the variations of the velocity of the wind. It is certain that the bird gains in the ascending currents of the air; but there have been noted also many sailing flights with the wind horizontal or even descending; so that if the theory of the ascendant wind suits very well certain cases, as also that which utilizes the variations of velocity and direction of the wind, there remains to be found a general theory which may be applied to all these different cases.
The sailing bird, having only the aid of the wind to support it in the air, must be built for utilizing the slightest current of air from whatever direction it comes. It is necessary also that its organs be delicate enough to adapt it without delay to the changes of the direction of the wind which are almost always very sudden. These results are assured by the suppleness of the wings themselves and by that of the feathers, since the position of the plane to the air has to be modified. In fact each change of direction of the wind requires, if the wings are not sufficiently supple, an oscillation of the body and of the wings all together. This is what is produced in the semi-sailing birds with the wings relatively rigid, the tips of which are convex and predominant as in the case of the sea gull and swallow.
Fig. in. Vulturk Soaring.
There results in these birds a sort of balancing very clearly noticeable to observers. This balancing is very much diminshed in large sailing birds with supple wings; the shifting of the wings comes into play and as the total mass of the body and of the wings requires much greater energy in order to be displaced from its equilibrium, it is the wings alone that feel the effect of the changes of the direction of the wind. And when the variations of the wind are very slight, the feathers alone, the respective independence of which makes them like so many small wings for independent shifting, receive the puff of air and absorb its energy.
The large sailing birds having to count only upon the wind are necessarily constructed so as to utilize the lightest breath of air; everything with them tends to this result, from the sensitiveness of the feathers and the suppleness of the wing, to the ability of spreading the wing like a fan when, if they wish to rise, they have need to increase explains the different positions reproduced in our figures 4 and 8, the first corresponding to a light wind for the utilization of which it is necessary to set full sail, the other becoming necessary when the wind freshens and there is need of taking a reef. Between these two extreme cases, there is an infinity of intermediate situations that the shifting of the feathers, or that of the wings, if it is necessary, suffice to regulate. The quill-feathers, in fact, constitute an automatic shifting device which assures the longitudinal and lateral equilibrium in normal conditions; the assistance of the wing, and of the entire body, are used only in extremely violent strokes. This automatic shifting is indispensable to birds that practice flight by sailing, and those which are not provided with it, the
their sail. This
semi-sailers, are not as good flyers in high winds, unless they spread their wings like a fan as the stork in figure nine, in order to give a little independence to the extremities of the feathers. But this slight defect is not sufficient to destroy the brilliant qualities of flight which these birds present; powerful rowers, they are masters of the air, not being, like the large sailing birds, at the mercy of a dead calm, which is always possible and many render them powerless. In short, the latter have taken their qualities from the two extreme groups; the rowers and the sailers in order to
utilize them according to circumstances. It is then the semi-sailers much more than the sailers that practice the most perfect flight, and man's imitation, which is often a criterion, gives actual proof of this. The aeroplane as it is conceived today, is only a semi-sailer with its screw propeller which allows it to take flight and sustain itself in the air, with its supporting and shifting planes, and its rudder which directs it. This gives us a hope that the day is not distant when automatic action will enable the machine to practice the true sailing flight without the aid of any motor whatever.
On a Bust of Dante
The lips as Comae's cavern close,
The rigid front, almost morose,
Unsullied still, though still severe;
Which through the wavering days of sin,
Kept itself icy — chaste and clear.
Peace dwells not here — this rugged face
Betrays no spirit of repose;
The marble man of many woes.
Such was his mien when first arose
When, hell he peopled with his foes,
—T, W. Parsons.
THE bumblebee is to be rendered almost superfluous in nature by a machine newly patented by an Indiana inventor—James M. Dennis, of Cambridge City.
This, at all events, so far as concerns clover and alfalfa plants, which have depended almost wholly upon the bumblebee for their production of seed. Where there are no bumblebees there is neither clover nor alfalfa. Which is why our government, not long ago, sent several batches of these useful insects to Australia, a bumblebeeless and cloverless country.
Up to date, it does not appear that the experiment has "panned out" as well as
was expected. But this is a matter of no importance if the "fecundating machine," as the inventor calls it, works as well as he claims it does. One such machine, he asserts, is equal for fertilizing purposes to a whole swarm of bumblebees.
The contrivance is a two-wheeled skeleton cart, and is intended to be driven by a man over a clover field. In the rear of the axle is a horizontal frame extending almost the entire width of the vehicle. This frame is interlaced with numerous wires in such fashion as to divide it up into an arrangement of square meshes.
It will be understood, then, that the interlacing wires join each other at right
cart wheels, they are lifted gently and dropped suddenly. This keeps the frame continually agitated; likewise the fuzzy fingers, which brush the blossoms, take up their pollen, and deposit it upon other blossoms.
In order that clover or alfalfa shall produce good seed, it is necessary that the blossoms shall be cross-pollinated. In other words, the pollen of one blossom must fertilize another. This is a task satisfactorily accomplished by the bumblebee; but Mr. Dennis claims that his machine does it equally well, and that it can be relied upon to fertilize practically all the blossoms in any patch.
A smaller machine is also being made now for similar use among strawberry plants.