16 Prof. Forbes 1 s Researches on the Vibrations which talc place 



paper, entitled " Notice regarding some Phenomena observed 

 during the Cooling of certain Metals placed in contact with 

 Lead." This was the first account published of the remark- 

 able discovery made by that gentleman, of a most curious 

 class of phnenomena, which till then was unknown to the sci- 

 entific world. This paper was afterwards published, with 

 some additions, in the 12th volume of the Transactions of that 

 body, under the title of" Notice regarding some Observations 

 on the Vibrations of Heated Metals*." 



2. Mr. Trevelyan had, in February 1829, first observed the 

 phaenomena just alluded to, which consist in certain tremulous 

 motions accompanied by sounds, often highly musical, excited 

 in many metals while hot, placed in contact with lead or tin, 

 at a lower temperature. The method of rendering these con- 

 spicuous will be understood from fig. 1, where A represents 



Fiff. 1. 



a block of lead, and B a bar of some other metal, such as 

 brass or copper, which is made of such a form as to vibrate 

 readily upon two points of support, formed by the solid angles 

 of a ridge left on its lower surface, which is bevelled away on 

 either side. The narrower this ridge, of course the more 

 easily the equilibrium is disturbed. No sooner is the bar of 

 copper, iron, or other hard metal, placed upon the lead-block, 

 the former being heated to a moderate temperature, than visi- 

 ble vibrations commence, the bar oscillating upon its hori- 

 zontal axis. Musical notes are not always produced, but 

 generally under the circumstances shortly to be noticed. Soon 

 after Mr. Trevelyan's communication to the Royal Society of 

 Edinburgh, the subject was taken up by Professor Leslie and 

 Mr. Faraday, both of whom explained the vibrations upon 

 recognised principles, and did not conceive that any new mode 

 of action was concerned in their production. Doubts which 

 1 ventured to entertain as to the conclusions of these eminent 

 individuals, led me to investigate the subject experimentally, 

 by which these doubts were strongly confirmed. Facts in- 

 creased in number, and 1 was forced to abandon several suc- 



* See also Lend, and Edinb. Phil. Mag., vol. iii. p. 321. 



