236 Mr. Wheatstone on the 



the intensity will be at its maximum, and when they are per- 

 pendicular to each other, at it's minimum; thus, supposing the 

 sound to commence when the two planes are parallel, it will 

 gradually diminish until they make an angle of 90 ; it will 

 then increase through the same changes of intensity, in an 

 inverted order, until it acquires its maximum at 180; it will 

 again decrease between this and 270, and increase until it 

 arrives at its first position at 0. If the stem of the tuning- 

 fork be placed perpendicularly on the side of a conducting- rod 

 resting on a sounding-board, the same phenomena may be 

 observed ; the stem of the tuning-fork is, in fact, a short con- 

 ductor, forming a right angle with the rod. 



Were it necessary for the transmission of sound that the 

 undulations should propagate themselves only rectilinearly, it is 

 obvious that they would not pass through a bent rod ; and, on 

 the other hand, had they the property of diffusing themselves 

 equally in all directions, we should not observe any differences 

 of intensity in the experiments above noticed. These expe- 

 riments lead us to conclude, that sound diffuses itself in all 

 directions, though unequally ; that it is communicated more 

 readily in the plane in which the original vibrations are made, 

 and with the greatest degree of intensity in the direction of 

 these vibrations. 



10. 



In most of the experiments relating to the transmission of 

 the sounds of musical instruments, which I have in the preced- 

 ing paragraphs detailed, the conductor has been represented 

 as receiving its impulses from a surface vibrating normally, to 

 which it was perpendicularly attached ; the communication 

 was consequently effected by longitudinal undulations in the 

 conducting wire. But if, while the conductor retains its posi- 

 tion, the surface were' to vibrate tangentially or obliquely, the 

 communication would be effected by transversal 'or oblique 

 undulations. 



In practice it is preferable to employ the longitudinal undu- 

 lations for the purpose of transmitting musical sounds to a 

 Distance; for, firstly, the transmission is more efficacious; 

 and, secondly, 'the transverse undulations have a great ten 



