2 Dr. Tyndall on the Vibrations and Tones produced by 



of the smaller Northumberland pipes, an instrument played by 

 his father's gamekeeper. Not knowing the cause of the sound, 

 he thought that this person might be practising out of doors ; 

 but on going out the tone ceased to be heard, while on his return 

 he heard it as shrill as before. His attention was at length 

 attracted to the hot iron, which he found to be in a state of 

 vibration, and thus discovered the origin of this strange music. 

 In 1830 he came to Edinburgh, and mentioned the fact to Dr. 

 Reid ; the latter, not knowing what Schwartz and Gilbert had 

 observed previously, regarded the phsenomenon as new, and re- 

 commended Mr. Trevelyan to investigate it more fully; Mr. 

 Trevelyan did so ; among other things he discovered the form 

 to be given to the vibrating mass (the rocker) in order to obtain 

 the effect with ease and certainty. The results of his numerous 

 and well-contrived experiments were communicated to the Royal 

 Society of Edinburgh, and were subsequently printed in the 

 Society's Transactions. 



On the 1st of April 1831 these vibrations and tones consti- 

 tuted the subject of a Friday evening's lecture by Professor 

 Faraday at the Royal Institution. The following extract from 

 the Journal of the Institution (vol. ii. p. 120) informs us of the 

 views of the philosopher last mentioned with respect to the cause 

 of the tones : — "As the sounds were evidently due to the rapid 

 blows of the rocker, the only difficulty was to discover the true 

 cause of the sustaining power by which the rocker was kept in 

 motion, whilst any considerable difference of temperature existed 

 between it and the block of lead underneath. This power Pro- 

 fessor Faraday referred to expansion and contraction, as Professor 

 Leslie and Mr. Trevelyan had done generally. But he gave a 

 minute account of the manner in which, according to his views, 



such expansions and contractions could produce the effect 



The superiority of lead, as a cold metal, he referred to its great 

 expansibility by heat, combined with its deficient conducting 

 power, which is not a fifth of that of copper, silver or gold ; so 

 that the heat accumulates much more at the point of contact in 

 it than it could do in the latter metals, and produces an expan- 

 sion proportionably greater." 



Professor J. D. Forbes was present at this lecture, and by it, 

 apparently) he was induced to undertake the further examination 

 of the subject. On the 18th of March and on the 1st of April 

 1833 the results of his inquiries were communicated to the Royal 

 Society of Edinburgh. He dissents from the explanation sup- 

 ported by Professor Faraday. The vibrations, he urges, are de- 

 pendent for their existence on the difference of temperature of the 

 two surfaces in contact ; if then the heat accumulate at the sur- 

 face of the cold metal^ its effect will be to bring both surfaces to 



