224 Royal Institution. 



ing-works of Saxony, placed a cup-shaped mass of hot silver upon a 

 cold anvil, and was surprised to find that musical tones proceeded 

 from the mass. In the autumn of tlie same year, Professor Gilbert 

 of Berlin visited the smelting-works and repeated the experiment. 

 He observed that the sounds wei"e accompanied by a quivering of 

 the hot silver ; and that wlien the vibrations ceased, the sound 

 ceased also. Professor Gilbert merely stated the facts, and made 

 no attempt to explain them. 



In the year 1829, Mr. Arthur Trevelyan , being engaged in spread- 

 ing pitch with a hot plastering-iron, and once observing that the 

 iron was too hot for his purpose, he laid it slantingly against a block 

 of lead which chanced to be at hand ; a shrill note, which he com- 

 pared to that of the chanter of the small Northumberland pipes, 

 proceeded from the mass, and on nearer inspection he observed that 

 the heated iron was in a state of vibration. He was induced by 

 Dr. Reid of Edinburgh to pursue the subject, and the results of his 

 numerous experiments were subsequently printed in the Transac- 

 tions of the Royal Society of Edinburgh. 



On the 1st of April, 1831, these singular sounds and vibrations 

 formed the subject of a Friday evening lecture hy Professor Faraday, 

 at the Royal Institution. Professor Faraday expanded and further 

 established the explanation of the sounds given by Mr. Trevelyan 

 and Sir John Leslie. He referred them to the tapping of the hot 

 mass against the cold one underneath it, the taps being in many 

 cases sufficiently quick to produce a high musical note. I'he alter- 

 nate expansion and contraction of the cold mass at the points where 

 the hot rocker descends upon it, he regarded as the sustaining power 

 of the vibrations. The superiority of lead he ascribed to its great 

 expansibility, combined with its feeble power of conduction, which 

 latter prevented the heat from being quickly diffused through the 

 mass. 



Professor J. D. Forbes of Edinburgh was present at this lecture, 

 and not feeling satisfied with the explanation, undertook the further 

 examination of the subject ; his results are described in a highly 

 ingenious paper communicated to the Royal Society of Edinburgh 

 in 1833. He rejects the explanation supported by Professor Faraday, 

 and refers the vibrations to " a new species of mechanical agency in 

 heat" — a repulsion exercised by the heat itself on passing from a 

 good conductor to a bad one. This conclusion is based upon a 

 number of general laws established by Professor Forbes. If these 

 laws be correct, then indeed a great step has been taken towards a 

 knowledge of the intimate nature of heat itself, and this considera- 

 tion was the lecturer's principal stimulus in resuming the examina- 

 tion of the subject. 



He had already made some experiments, ignorant that the subject 

 had been further treated by Seebeck, until informed of the fact by 

 Professor Magnus of Berlin. On reading Seebeck's interesting 

 paper, he found that many of the results which it was his intention 

 to seek had been already obtained. The portion of the subject 



