C. GENERAL PHYSICS. 181 



is dependent on the elasticity of the air-column of the pipe 

 and the pressure of the outer air, and so is subject to the laws 

 of vibration of the air-column. Poggendorff''s Aimalen^l^lQ. 



OBLITERATION OF ONE SOUND BY ANOTHEK. 



Mayer, in the eighth series of his researches on acoustics, 

 communicates certain striking results which he has obtained 

 on the obliteration of one sound by another, from which he 

 draws conclusions as novel as they are important. The in- 

 vestigation was suggested by observing the ticks of a watch 

 .making live per second, in conjunction with those of a loud- 

 ticking clock making four ticks per second. On regulating 

 the distance of the watch the fifth tick became fainter, until 

 it disappeared entirely. An old silver watch, making four 

 ticks per second, was then made to gain thirty seconds an 

 hour on the clock, so that at every two minutes the ticks of 

 the two coincided. When the watch was held at nine inch- 

 es from the ear, its ticks were wholly obliterated for three 

 seconds ; and when at twenty-four inches, for nine seconds. 

 As the time of coincidence approached, the short ticks of the 

 watch glided tick after tick under the long ticks of the 

 clock, more and more of the duration of each successive 

 watch-tick became extinguislied by the tick of the clock, un- 

 til only the tail end of the short tick of the watch was left 

 audible ; and at last even this also crept under the long tick 

 of the clock, and the whole of the ticks of the watch were 

 rendered inaudible for nine seconds, at the end of which time 

 the front or head of the watch-tick protruded beyond the 

 clock-tick, and then slowly grew up into a complete watch- 

 tick as before. Experiments were then made to measure the 

 relative intensity of the two ticks, by placing both succes- 

 sively in the open air during a still night, and observing the 

 distance at which they could be heard. The general result 

 shows that the sensation of the watch-tick is obliterated by 

 a coincident tick of the clock when the intensity of the clock- 

 tick is three times that of the watch-tick. Extending: the 

 observations to musical sounds, Mayer observed in general 

 tlie same phenomena. But he discovered here the new and 

 remarkable fact that a sound higher in pitch than another 

 can not obliterate it, no matter how intense. A curious ef- 

 fect of this law is observed if, while a man reads a sentence 



