114 



Mr. G. H. Berry on 



3 



no part in communicating the vibrations o£ the string to the- 

 sound-board. It is used to determine the vibrating length 



of the string and the striking-point of the hammer. 



Some experiments with the other or free bridge are recorded 



in this paper. 



The construction of the pianoforte may be illustrated by 



fig. 1. The iron frame is omitted for the sake of clearness. 



A is a heavy beam of wood, holding B, B', 



pieces of beech into which the tuning-pins Fig. 1. 



C, C are driven. D is the sound-board, 



supported by the fillets E, E'. The sound- 

 bar F is glued to the back of the sound- 

 board. G is the fixed and H the free bridge. 



The steel string K passes between two iron 



pins driven into the free bridge H : these 



pins are not parallel but dip towards one 



another, and hold the string on the bridge 



but do not prevent it from sliding over the 



face of the bridge when the string is being 



tuned. The part of the string between H 



and is technically called the back-wire, 



and is permanently damped by a piece of 



baize. The vibrating length of string is 



that portion between G and H, and when 



struck with a pianoforte hammer it is forced 



towards the sound-board. 



There are three different ways in which 



the vibration of the string may be trans- 

 mitted to the sound-board through the free 



bridge. 



(1) Any deflexion of the string will ob- 

 viously cause a pull upon the free bridge H 

 in a direction parallel to the string and 

 towards the fixed bridge G. The move- 

 ment of the bridge will be transmitted to 

 the sound-board, deflecting it towards the 

 back wire in the upper half and away from 

 the string in the lower half. As the string 

 comes back to its normal position the bridge and sound- 

 board will also be allowed to return, but as the string swings 

 out and away from the sound-board the bridge will again 

 be subject to a pull parallel to the string, and the sound- 

 board will be deflected in the same way as during the first 

 movement of the string. In this way, the bridge and sound- 

 board will have a frequency twice that of the string but, 

 as the sound we hear comes from the sound-board and not 



a 



c 



