420 GENEKAL SCIENCE 



Fasten the wires to these screws and tighten the wires by turning the screws 

 until they produce the same pitch. This instrument is called a sonometer. 



Place on one string a piece of paper folded into a " V" shape, called a rider. 

 Set the other string vibrating. If the two strings are tuned exactly alike, 

 the string with the rider on it will begin to vibrate sympathetically. 



2. Stand in an empty room and produce a sound, gradually changing the 

 pitch until the correct pitch is struck. The empty room will then seem full 

 of sound. If the room is round or has a spherical ceiling, a great deal of sound 

 will be obtained. All corners, angles, and pockets will respond when the proper 

 pitch is struck. Not only do empty rooms respond to the proper pitch, called 

 the fundamental or natural tone, but also to its harmonics, the third and fifth 

 tones, which will be about one-half as loud. If the fundamental is do the third 

 harmonic is me and the fifth sol. 



3. Release the loud pedal on the piano and strike the key C. Immedi- 

 ately place a finger on the strings of C which are vibrating and listen to the 

 sympathetic tones produced. 



If two tuning forks of the same pitch be placed at the right distance apart, 

 and one fork caused to vibrate and then suddenly stopped, the other fork will 

 be heard producing a sympathetic tone. 



Sympathetic Noise. Very often a piece of metal is caused to 

 rattle by the playing of some note on the piano or the sound vibra- 

 tions produced by a cornet. Teaspoons in a glass holder or in a 

 pan may rattle enough to be heard some distance. A piece of metal 

 like a teaspoon, ring, or pair of scissors placed on a table may also 

 produce sympathetic noise if the right pitch is struck. 



Piano tuners may experience difficulty in tuning a piano because 

 of a vase or other object in the room which may vibrate in sympathy 

 with some tone. 



Experiment. Fasten a small pan to a spring and wire by attaching a pail 

 to the pan. Fasten the wire to the ceiling or to some convenient object so that 

 it will move freely. Place a few pieces of shot or small pebbles or coarse sand 

 in the pan. Blow on a cornet, changing the pitch until the material inside the 

 pan is made to jump about. This experiment illustrates sympathetic noise. 



Sympathetic Vibration of Tuning Forks. If two tuning forks, 

 fastened to resonance boxes as shown in the illustration, are placed 

 at the proper distance apart, the sound waves will vibrate in perfect 

 conjunction, and the sound produced will be twice as loud as that 

 produced by one fork. If the forks be placed at such a distance 

 that the two sound waves do not meet in perfect conjunction, the 



