266 PHENOMENA OF FLIGHT IN THE ANIMAL KINGDOM. 



muscle, is placed a little contrivance intended to exhibit tlie swelling of 

 the muscle. It consists of a small, shallow metal basin containing a 

 spiral spring and is closed over by a thin sheet of rubber. This basin, 

 thus closed, communicates with the transmitting tiibe. 



Any pressure applied to the 

 face of the api)aratus depresses 

 the rubber. The air is forced 

 out of the basin and escapes by 

 the tube. If the ])ressure ceases, 

 the air reenters the basin in con- 

 sequence of the elasticity of the 

 spring which raises the rubber. 

 An alternate inspiration and as- 

 piration is bv this means estab- 

 lished in the tube, and the mo- Apparatus for exhibiting the contraction of 

 ^ ., . ' -^ - .1 the thoracic muscles or birds. Ihe upper con- 



tion Ot the air transmits to the vex face is formed of a sheet of rubber, held 

 registering apparatus a signal of up by a spiral spring, and is applied to the mus- 

 the more or less intense pressure cles. The lower face, in contact with the cor- 



which has been exerted upon the ^f ' ^fYi'" ^''"^"^[,"6 hooks which are caught in 



, , n ., ■, • mi the cloth and hold the apparatus m its place, 



rubber cover of the basin. The 



registering apparatus I have used in all my experiments is also com- 

 I)osed of a basin, covered by a rubber membrane communicating with 

 the transmitting tube. The motion imparted to the first basin is 

 transmitted by the air to the rubber cover of the second. The motions 

 of the membrane of the receiving apparatus, amplified by a lever, are 

 written on the smoked cylinder. Figure 10 represents the general 

 arrangement of the experiment in which the electric telegraph and trans- 

 mission by air are exhibited together. We see the pigeon under ex- 

 periment furnished with its corset and apparatus for showing the move- 

 ments of its pectoral muscles. The transmitting air-tube ends at the 

 registering apparatus, which writes on a revolving cylinder. At the 

 extremity of the i)igeon's wing is an arrangement which opens or closes 

 an electric circuit as the wing rises or falls. The two wires of the cir- 

 cuit are represented separately, and two cells of Bunsen's battery are 

 seen in their connection, with the helix, which, furnished with a lever, 

 registers the telegraphic signals of the motions of the wings. One pre- 

 caution is indispensable — the rubber tube which connects the bird and the 

 apparatus must be prevented from stretching. When the bird flies it 

 raises more or less of the tube, and if this is elastic it will become elon- 

 gated by its own weight, producing a rarefaction of the air contained 

 in the two receptacles, and the registering lever will trace muscular 

 curves on a decending line. To prevent this inconvenience, the tube 

 may be tied here and there to the telegraphic cord by means of ligatures, 

 taking care that the tube is a little longer than the cord, and that 

 it is not subjected to traction. These precautions- being taken, nothing 

 jjrevents the successful transmission of signals. Ko trouble need be 

 taken in regard to the elasticity of the tube in a transverse direction ; 

 its walls are so thick that their elasticity is not brought into play by the 

 feeble changes of pressure to which the air they contain is subjected. 



The bird is let loose at one end of the inclosure, the dove-cote in which 

 it is ordinarily kept being placed at the opposite end. The bird 

 naturally flies toward the latter. During its flight the tracings repre- 

 sented by Fig. 18 are obtained. 



The trace is seen to differ according to the kind of bird experimented 

 upon. However, in all the traces we perceive the periodical return of 

 two motions, a and b, which are i)roduced in each vibration of the wing. 



