Mr Weber on the Polarisation of Sound. 9 



of the instrument. For, as in this case, the broad, as well 

 as small sides of a common pitchpipe have smooth simple 

 edges, as was the case with a triangular pitchpipe with which 

 several experiments were made ; the strength of the spreading 

 of the tone shows itself by turning one of these edges to the 

 ear in the same manner as when the side was turned into that 

 position. 



On the contrary, the tone will be weaker, if the broad and 

 small surfaces of the branches of an usual pitchpipe, ha vino- 

 carved edges, is directed to the ear ; and, in a particular 

 direction, (about the direction of the diagonal of a right angle 

 which terminates the upper end of the branches,) the tone is 

 extinguished altogether. This extinction of the tone, and the 

 position in which it takes place, depends upon the relation be- 

 tween the breadth and thickness of the branch, but it is inde- 

 pendent of the form and position of the terminating sides of 

 the branch, in the same manner as the appearance of the in- 

 creased strength of the sound was independent of the two 

 right-angled arrangements placed under each other. For 

 when, in the place of the edge of the common pitchpipe, sides 

 are presented similar to those in the triangular pitchpipe, the 

 vanishing of the tone takes place when one of these sides is 

 turned to the ear. 



In the same manner, the tone is heard when the two small 

 right angles is turned to the ear, which terminate the end of 

 the branch of the pitchpipe of the usual form. If we gradually 

 turn the pitchpipe round one of these right-angled terminat- 

 ing edges, as if round an axle, so that one lateral surface of the 

 pitchpipe begins to turn to the ear, the tone becomes weaker, 

 and, in a particular position, entirely vanishes — again reappears 

 in continuing to turn, and reaches its greatest strength when the 

 lateral surface is completely parallel with the shell of the ear. 

 This appearance does not arise from the varying influence of 

 the two turning branches ; since it takes place when one branch 

 is entirely separated from the other branch, by being covered 

 with a tube. 



