448 Prof. FORBES on the Vibrations which take place 



brated precisely as if the entire bar had been made of copper. In 

 an early part of this paper I described an experiment, in which 

 the points of the block upon the bar impinged, were completely 

 distinct pieces of metal; See Fig. 3. We therefore conclude 

 that the impulse is received by a distinct and separate process at 

 each contact of the bar with the block, and that in neither case is 

 the connection of these points in any way essential. 



39 . The use of bars made entirely of the different metals is 

 therefore quite unnecessary. A convenient form of experimen- 

 tal apparatus is suggested, by the following construction, which I 

 have employed with success. A heated ring of brass or copper, 

 three or four inches in diameter, being placed side ways upon a ridge 

 of solid lead, with two solid angles, upon which the ring may vi- 

 brate (the plane of the ring being horizontal), the action will be 

 extremely energetic, the impulse being given simultaneously at 

 two points, as shewn in Fig. 6. If we had the means of firmly 

 clamping two slips of any metal under experiment to the two 

 points of the ring in contact with the block, by means of tighten- 

 ing screws, so as to substitute the material required for that of 

 which the ring is made, we should have a convenient apparatus, 

 requiring very small pieces of the metals to be tried, and there- 

 fore well adapted for experiments on gold, silver, &c. 



40. The influence of the thickness of the metals employed, 

 and of the extent through which the impulse may be given, 

 early attracted my notice ; and I found that thin films of metals 

 of superior conducting power, in the form of leaf, burnished upon 

 the lead block, did not annihilate its characteristic property. 

 The same result in regard to simple gilding was announced by 

 Mr TREVELYAN. 



41. We have now to resume the consideration of an import- 

 ant point connected with figure, referred to in an early part of 

 this paper ; I mean the groove in the bar or block, which fre- 

 quently appears essential to the production of a musical note. 



