Mr. A. Trevelyan on the Vibration of heated Metals. 3'25 



weight on each side, which assists the vibration : the longitu- 

 dinal ridge is the part that rests on the block, (figs. 3 & 4.). 



A hollow lead cylinder about J an inch thick, with the dia- 

 meter in proportion to the length of the bar, is the best form 

 for showing the vibrations and producing the tone. 



An inequality or unequal notch on the lead cylinder in- 

 creases the sound. When the bar at a high temperature is first 

 placed on the cold lead, the tone is very harsh and undefined; 

 but when the lead has acquired a certain proportion of heat, 

 it becomes clear, full and mellow. 



Pressure on the bar alters the note : the greater the pres- 

 sure the higher is the note. Pressure also applied to the 

 sounding-board or table on which the vibrating bar may 

 happen to be placed, or even walking across the room, by al- 

 tering the position of the bar, changes the tone. 



A common poker heated and placed on a lead block vi- 

 brates, producing deep tones. If the vibrating bar be placed 

 on a piano-forte, and certain notes be struck on the instru- 

 ment, the vibration of the bar, and consequently the tone pro- 

 duced by it, is altered, and sometimes suddenly stopped. 



Vibration is prevented by rubbing the surface of the lead 

 with mercury, oil, plaster of Paris, or by oil gilding ; also if a 

 piece of thin tissue paper, or of wire-gauze, be interposed be- 

 tween the bar and the block. 



The vibrations have not been produced with any substances 

 besides metals, except in the instance of the glass tumbler al- 

 ready mentioned. 



To try whether there was any attraction between the hard 

 and soft metals when heated, I had two pieces of brass, about 

 the size of an ounce weight, with a wire attached to them, and 

 then hung on a delicate scale beam : having heated the brass 

 weights, blocks of lead were placed under them and tried at 

 various distances, but without producing the slightest effect. 



To try whether electricity caused the phenomenon or made 

 any alteration whilst the bar was vibrating, a hole was drilled in 

 a bar and filled with mercury, a wire was soldered to the lead 

 cylinder on which it was placed, and a galvanic battery of 

 150 plates, 4 inches square, being charged, the wire from the 

 cylinder was placed in one end of the battery, whilst from 

 the other end a wire was brought to the mercury contained 

 in the cavity of the bar, which was heated, and in motion, pre- 

 vious to completing the circle. We also tried other methods, 

 but with none of them did we succeed in producing any change 

 either in the tone or in the vibration. 



A Leyden phial was charged with electricity, and applied 

 to the same bar and block, without producing any effect. 



