740 THE POPULAR SCIENCE MONTHLY. 



experiment for the entertainment of his guests and his own. profit. 

 The nightingale is said to kill by the power of its notes. The bark of 

 a dog is able to call forth a response from certain strings of the piano. 

 And a curious passage has been pointed out in the Talmud, which dis- 

 cusses the indemnity to be claimed when a vessel is broken by the 

 voice of a domestic animal. If we enter the domain of music, there 

 is no end to the illustrations which might be given of these sympathetic 

 vibrations. They play a conspicuous part in most musical instru- 

 ments, and the sounds which these instruments produce would be 

 meagre and ineffective without them. 



In the case of vibrations which are simply mechanical, without 

 being audible, or at any rate musical, the following ocular demonstra- 

 tion may be given : A train of wheels, set in motion by a strong 

 spring wound up in a drum, causes an horizontal spindle to revolve 

 with great velocity. Two pieces of apparatus like this are placed at 

 the opposite sides of a room. On the ends of the spindles which face 

 one another are attached buttons about an inch in diameter. The two 

 ends of a piece of white tape are fastened to the rims of these buttons. 

 When the spindles, with the attached buttons, revolve, the two ends of 

 the tape revolve, and in such directions as to prevent the tape from twist- 

 ing, unless the velocities are different. Even if the two trains of wheels 

 move with unequal velocities, when independent of each other, the 

 motions tend to uniformity when the two spindles are connected by 

 the tape. Now, by moving slightly the apparatus at one end of the 

 room, the tape may be tightened or loosened. If the tape is tight- 

 ened, its rate of vibration is increased, and, at the same time, the ve- 

 locity of the spindles is diminished on account of the greater resist- 

 ance. If the tape is slackened, its rate of' vibration is less, and the 

 velocity of the spindles is greater. By this change we can readily 

 bring the fundamental vibration of the tape into unison with the ma- 

 chinery, and then the tape responds by a vibration of great amplitude, 

 visible to all beholders. If we begin gradually to loosen the tape, it 

 soon ceases to respond, on account of the twofold effect already de- 

 scribed, until the time comes when the velocity of the machinery ac- 

 cords with the first harmonic of the tape, and the latter divides beau- 

 tifully into two vibrating segments with a node at the middle. As 

 the tension slowly diminishes, the different harmonics are successively 

 developed, until finally the tape is broken up into numerous segments 

 only an inch or two in length. The eye is as much delighted by this 

 visible music as the ear could be if the vibrations were audible ; and 

 the optical demonstration has this advantage, that all may see, while 

 few have musical ears. A tape is preferred to a cord in this experi- 

 ment, because it is better seen, and any accidental twist it may ac- 

 quire is less troublesome. 



