326 Mr. A. Trevelyan on the Vibration of heated Metals. 



Spirit of wine, or aether, evaporated off the heated bar when 

 in motion, produced no effect. 



Air blown with a pair of bellows on the heated bar when 

 vibrating does not affect the tremors. 



If the heated bar be ground smooth, on the resting part, 

 and the block of lead be also very smooth, no vibration takes 

 place. 



When the bar and block become of the same temperature, 

 the vibration and sound cease. 



A cylinder, 5 inches Jong, with a thick side bevelled off, 

 leaving a flat ridge in the centre, similar to the former bars, 

 when heated and placed on lead, produced no change of tone. 



From the above-related experiments it appears : 



1st, That in order to produce the vibrations, metals must 

 be employed, either of the same kind or different, for both the 

 bars and blocks ; with the single exception of the glass tumbler. 



2nd, That the difference of temperature between the two 

 metals must be considerable, although some require a much 

 higher temperature than others: the vibrations on zinc and 

 bell-metal succeed with a lower temperature than others of 

 the hard metals. 



3rd, That the surface of the block must have some degree 

 of unevenness, for when rendered quite smooth, the vibration 

 does not take place ; but the bar cannot be too smooth. 



4th, That the interposition of any matter prevents vibra- 

 tion, with the exception of a burnish of gold-leaf, the thick- 

 ness of which cannot amount to the 200,000dth part of an 

 inch. 



5th, That the air has no share in the production of the 

 vibratory movements, however much its presence is essential 

 to the production of sound. 



6th, That it has no connexion with galvanism or electri- 

 city, the vibration and tone not being affected by passing a 

 current through the bar when in action. Professor Forbes 

 found no appearance of thermo-electricity after trying a num- 

 ber of experiments. 



7th, That all the metals, both simple and alloys, produce 

 vibration and sound, when one is heated and the other cool, 

 on being brought into contact, (with the exception of bismuth,) 

 but with some we find much greater difficulty in obtaining vi- 

 bration than in others, as it depends on the temperature, but 

 more particularly on the mode of placing the one on the other, 

 which with some requires great nicety. 



8th, Although all the metals are not found to vibrate on 

 each other, or on metals of the same kind, — and I have not 

 been able produce vibration with other substances, — yet I do 



