236 



ANIMAL MECHANISM. 



understand the construction of the machine which we finally 

 employed. 



On two solid feet carrying vertical supports, we placed 

 two horizontal arms parallel to each other. These were two 

 aluminium levers, which, by means of the apparatus we are 

 about to describe, will both execute the same movements. 

 Each of these levers is mounted on a Cardan joint, that is to 

 say, a universal joint which allows every kind of movement ; 

 so that each lever can be carried upwards, downwards, to 

 the right or the left ; it can describe with its point the base 

 of a cone of which the Cardan forms the apex ; in fact it will 

 execute any kind of movement which the experimenter may 

 please to give it. 



It was requisite to effect the transmission of the move- 

 ments of one of these levers to the other, and that at a dis- 

 tance often or fifteen metres. This is done by a method with 

 which the reader is already acquainted — the employment of 

 air-drums and tubes. 



The lever, which in fig. 97 is seen to the left hand, is 

 fastened by a vertical metallic wire to the membrane of a 

 drum placed underneath it. In the vertical movements of 

 the lever, the membrane of the drum, alternately depressed 

 and raised, will produce a current of air, which will be trans- 

 mitted by a long air-tube to the membrane of a similar drum 

 belonging to the apparatus on the right hand. The second 

 drum, placed above the lever which corresponds with it, and 

 is fastened to it, will faithfully transmit all the vertical 

 movements which have been given to drum No. 1 (that on 

 the left). The motion of the two levers will be in the same 

 direction, on account of the inversion of the position of the 

 drums. 



Let us suppose that we lower the lever No. 1 ; we com- 

 press the membrane of the drum beneath it; a current of 

 air is produced which raises the membrane of the second 

 drum, and consequently lowers lever No. 2. On the contrary, 

 the elevation of lever No. 1 will produce an inward current of 

 air, which will raise the membrane and the lever of No. 2. 



Proceeding in the same manner for the transmission of 

 movements in the horizontal plane, we place to the right of 



