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turns, would give lateral movements to the pivot on which it rests, and to the base itself.

To furnish the bird with a solid point of suspension, protected not only from vertical oscillations, but from movements of torsion, we have placed at each end of the instrument a cross piece of wood, to the two extremities of which are attached cords communicating with the ceiling of the room. At this point is a revolving hook, which turns freely with the machine.

Of the apparatus which suspends the bird.-Fig. 104 shows the details of this suspension which binds the bird to the arm of the instrument, while it confines as little as possible the liberty of its movements.

Of the registering apparatus.-The transmitting tubes are arranged along the arm of the instrument; they are fastened to it throughout all its length, and end in a register which carries three lever-drums tracing on the revolving cylinder. The instrument in its rotation would cause the transmitting tubes to roll round its axis, if the register to which they are directed did not participate in the general rotation.

We see in fig. 103 how this apparatus is arranged. The cylinder is placed vertically above the axis of the instrument; the three levers trace upon it. The whole apparatus rests on a tablet, which turns on the central pivot. We have here well-known arrangements, in which several movements are registered at the same time on the cylinder; it will, therefore, be useless to repeat the precautions which are to be taken in the management of the apparatus, such as the exact superposition of the tracing points, &c.

The movements of the wing are extremely rapid; they can be registered only on a cylinder turning with great velocity; that which is employed in this experiment makes one revolution in a second and a half. The shortness of the time at our disposal to trace the movements of the bird compel us to do so only at the precise moment when the phenomena which we wish to observe are presented, whether it be the swiftest flight, the gradual slackening of its speed, or the efforts made at starting. If the three levers were to rub constantly on the cylinder, we should soon have nothing but a confused

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Fro. 104-Suspension of the bird in the instrument. EEEE. an ellipse of metal capable of oscillating freely in every direction, by means of the double suspension A. SS, india-rubber supports allowing the lower part of the ellipse to oscillate in the vertical direction. The suspensory apparatus is fixed on the back of the pigeon. The leverdrum (1) receives the movements executed by the wing in a vertical direction. The lever-drum (2) receives those of the horizontal movements.

scrawl. It is indispensably necessary so to arrange the instrument that the points of the levers should touch the cylinder only at the moment when we wish to register the phenomena, and to cease this contact after one, or at most two revolutions of the cylinder, in order to avoid confusion in the tracings.

We have recourse, for this purpose, to the arrangements already made in our experiments upon walking.

Fig. 103 shows the experimenter at the instant when he is about to take a tracing from the pigeon. Observing the flight of the bird, he seizes the moment when it becomes regular, and squeezes the india-rubber ball. The contact of the levers is immediately produced, and the tracing is made. After a second and a half he ceases to press it, the spring removes the levers from the cylinder, and the tracing is over.

With a little practice it is very easy to ascertain the duration of the revolution of the cylinder, and to confine the tracing to the necessary length.

This long description was necessary, as we were anxious to make this apparatus understood, it being the most important of all, on account of its double function. We shall have to employ it, not only in the analytical, but also in the synthetical part of these studies, when we shall attempt to represent the movements in the bird's flight.

New determination of the trajectory of a bird's wing.-A pigeon was made use of in this experiment. It was a male bird of the variety called the Roman pigeon, very vigorous, and accustomed to fly.* Fig. 104 shows the arrangement of the apparatus which we have used for the purpose of studying its movements.

It is more especially to the humerus that we have directed our attention, in order to obtain the movements of the wing in space. For this purpose a wire is twisted round the bone, holding it as in a ring, and furnishing by its free ends a firm point of attachment outside the wing for other wires which act on the experimental drums.

* This latter point is of great importance, for the greater part of the birds in a dove-cot are of no use to us, on account of their inexperience in flight.

The movements of the two wings being perfectly symmetrical in regular flight, we cause two wires, which pass symmetrically from the wings, to converge to each of the experimental drums. Thus, drum No. 1, intended to give signals of the elevation and depression of the wing, receives two wires, each of which proceeds from one of the humerus bones of the pigeon, at about 3 centimetres outside the articulation of the shoulder. These wires rise and converge, and are attached to the point of the lever No. 1; while from the same point proceeds an india-rubber thread,* which serves as a counter-spring, and rises vertically to a hook above, which holds it.

We have before seen (fig. 102) how the lever of the experimental drum receives, under these conditions, all the movements of elevation and depression executed by the humerus of the bird.

Two other wires, each attached to the humerus of the pigeon on each wing, and starting from the same point of the bone to which were fastened the wires of drum No. 1, converge also, turning backwards, and proceed to the lever of drum No. 2. This is the drum which receives the movements executed by the wing in the antero-posterior direction. The two drums send their signals by air tubes to the register situated in the centre of the apparatus.

Experiment.-After having ascertained that the two levers intended to trace have their points situated on the same vertical, the pigeon is allowed to fly. The bird goes through the movements of flight, and soon carries round with considerable rapidity the instrument to which it is attached. The operator, placed in the centre of the apparatus, has only to follow for a few paces the rotation of the instrument. During this time he holds in his hand the india-rubber ball, and has only to compress it, in order that the two levers may rest with their points against the blackened paper, and that the tracing may commence. As soon as the flight is well established, and seems to be carried on under satisfactory

* In fig. 104 a spiral spring has been substituted for this india-rubber thread.

conditions, he compresses the ball, and produces the tracing represented in fig. 105.

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Af

FIG. 105.-Tracing of the movements of a pigeon's wing. The upper line,
A P, shows the movements forwards and backwards. The lower line
H B, the movements up and down.

Interpretation of the tracings.-The curves are read from left to right, like ordinary writing. The upper curve is that described by the humerus of a bird in its movements forwards and backwards; the direction of these movements is indicated by the letters A and P, which signify that all the tops of the curves, as well as that at A, correspond with the time when the wing has reached the most forward part of its course; the lower parts of the curves, on the contrary, indicate, as well as that at the point P, the moment when the wing has reached the hinder part of its movement.

The horizontal line which cuts this curve has been traced in a previous experiment by the point of the lever at the instant when the wings of the bird, kept motionless by an

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