244 



Dr. W. Hugging. 



[May 24, 



There could be no doubt that vibrations were carried by the 

 clamp, for the lower end was powerfully agitated when the npper end 

 rested upon the belly. If the sole function of the sound-post is to 

 serve as a firm prop for the foot of the bridge, it should fulfil this 

 condition most fully when placed under the foot of the bridge. In 

 this position of the sound-post, however, as is well known, the tone is 

 much injured. 



In order to separate that part of the function of the sound-post 

 which serves as a support from the further function it may possess as 

 a transmitter of vibrations, it was desirable to introduce such altera- 

 tions in the structure of the sound-post as would enable it to retain 

 its supporting power, and yet greatly modify and, if possible, stop its 

 power of transmitting vibrations. A sound-post was made in which 

 about half an inch of the middle was cut out, and a piece of lead 

 inserted, also a sound-post in which instead of lead sealing-wax was 

 put in. The effect of these compound posts, which retained uninjured 

 their prop power, was to modify greatly the quality of the tone, but 

 not to diminish its quantity in any marked degree, a result in favour 

 of the view that the character of the wood of which the post is made 

 does influence the tone, and that vibration is transmitted by the post. 

 As these compound posts could transmit vibrations freely, it was 

 desirable to contrive a post which would not carry vibrations and yet 

 form a firm prop. A post was made with a piece of hard India- 

 Tubber inserted in the middle, but this post was found by experiment 

 with a tuning-fork to transmit vibrations to some extent. Other 

 materials were tried without success. A post capped at each end with 

 pieces of sheet vulcanized rubber stopped almost completely the 

 sound of a tuning-fork when the foot of the fork rested on the rubber 

 over one end of the post, while the other end equally protected with 

 rubber rested on a body capable of reinforcing the sound of the fork. 

 This rubber-capped post was firmly fixed in position in the violin, so 

 that it would be able to support fairly well the belly and foot of the 

 bridge, and yet not be able to carry vibrations ; unfortunately it does 

 not seem possible, from the nature of things, to have a rigid prop 

 which does not transmit vibrations, but this post with thin sheet 

 rubber at the ends firmly forced into position, must have been fairly 

 efficient in its supporting power. The effect on the tone was about 

 the same as when the sound-post was removed. When the wooden 

 clamp was put on, then the normal tone returned, and the back 

 vibrated strongly. 



These experiments appear to show that the sound-post is more than 

 a prop, and that besides its other functions, it does transmit vibrations 

 to the back in addition to those which are conveyed through the sides. 



Experiments with sand and the touch-rod appear to me to show 

 that Helmholtz's statement is too absolute when he says " it is only 



