150 Natural-Philosophical Collections. 



communicated to surfaces, as when the insulated string, or the tuning-fork is 

 placed on a table or on the sounding-board of a musical instrument. There are 

 several circumstances which influence the intensity of the tones of a sounding- 

 board : the principal of these is the plane in which the vibrations are made, with 

 respect to the reciprocating surface. Thus, the vibrations may be so communi- 

 cated as to be perpendicular or normal to the surface : in which case the sound 

 is the most greatly augmented ; or they may be tangential to, or in the same 

 plane with, the surface, when the sound is the most faint. These two cases may 

 be illustrated by placing, for the first, a vibrating tuning-fork perpendicular to, 

 the surface of a flat board ; for the second, placing it perpendicular to one of the 

 edges of the board. In intermediate positions, viz. when tlie vibrations are com- 

 municated obliquely to the surface, the sounds have intermediate degrees of in- 

 tensity. These facts being understood, the peculiarities of the sounding-boards, 

 of various musical instruments admit of easy explanation. In the piano-forte, 

 the sounding-board is better disposed than in any other instrument, as tlie planea 

 of the vibrations of the strings are always perpendicular to its surface. The dif- 

 ference of intensity when a string vibrates in this way, and when it vibrates par- 

 allel to the surface, may be easily tri^d. In the sounding-boards of the harp, the- 

 guitar, the violin, &c., the circumstances are less simple ; but it would encroach, 

 too much on our space to enter into details. Sufficient having been said to illus-. 

 trate the subsequent applications, we will only add, that the volumes of air con-, 

 tained between the sounding-boards of a musical instrument greatly augment the 

 intensity of the sound. The oflSce of the bridge is obviously to communicate the 

 vibrations of the strings to the sounding-board. Aware of this fact, Mr. Wheat- 

 stone substituted a glass rod five feet in length for the bridge, and found that the 

 sound of a tuning-fork, or of an insulated string, placed at its end, was as dis- 

 tinctly audible as when it was immediately in contact with the board. This ex- 

 periment, which was the first Mr. W. made on this subject, and which suggested 

 all the subsequent ones, was repeated in the lecture-room, by substituting a deal 

 rod forty feet in length, extending from the roof of the cupola to the floor of the 

 room. The experiment was neat and decisive. When no sounding-board was 

 placed at the lower extremity of the conductor, no sound was heard ; but it be- 

 came powerfully audible the instant the communication was made. This expe-. 

 ment was repeated with different acute and grave-toned tuning-forks, both in suc- 

 cession and in combination. As the sounds employed in these experiments are 

 only audible when they become augmented by resonant surfaces after transmis- 

 sion, it is easy to repeat them, and to appreciate their results, under any circum- 

 stances ; but when it is required to transmit the sounds of a musical instrument, 

 it is necessary to prevent the sounds being heard through the air, otherwise the 

 communicated sounds will not be distinguishable from the original sounds. This- 

 may be effected by having the originally vibrating and the reciprocating instru- 

 ments in different rooms, and allowing the conductors to pass through the floor 

 or wall separating the two rooms. This experiment was tried, by communicat-, 

 ijig, by means of a slender deal rod, the sounding-board of a harp in the lecture- 

 room with a piano-forte in a room below ; and the performance of the latter waa, 

 transmitted in the most perfect manner to the former instrument ; and when the 

 communication was interrupted, the transmitted sounds ceased. The construe-,- 

 tion of the lecture-room did not admit of the experiment being tried in the way^ 

 first employed by the experimenter ; viz. the sounds transmitted from a piano- 

 forte in a chamber above, by a wire of very small diameter, to a lyre suspended 

 from the ceiling. The transmission of the sounds of other stringed instruments, 

 such as the harp, violin, violoncello, &c., were found to be equally effective. But 

 Mr. W. did not confine his experiments to the transmission of the sounds of vi- 

 brating sounding-boards. He discovered also the means of transmitting the 

 sounds when produced from wind instuments. He observed that the peculiar 

 sounds of a clarionet, or other reed instruments, were not to be attributed either 

 to the column of air or to the vibrating tongue alone, but that they mutually in- 



