Solid Bodies when they are Sounded. 141 



This is probably due to the sound becoming so enfeebled by its 

 passage through the caoutchouc that its intensity is soon too 

 small to produce an appreciable increase. 



The only substance on which I did not succeed in obtaining 

 an increase of temperature by heat was glass. Thin glass tubes 

 put in strong vibration by resonance invariably cracked; and 

 with thick bars I could not observe a development of beat, pro- 

 bably because they could not be put in sufficiently powerful vi- 

 brations. 



Transversal Tones. 



From what has been said, alternate condensations and rare- 

 factions which occur in longitudinal tones are an essential con- 

 dition for heating to be produced by sound. Since condensations 

 and rarefactions are connected with the bendings which occur in 

 the case of transverse vibrations, an increase in temperature was 

 to be expected in transverse vibrations. This was indeed ob- 

 served ; yet there was a far more complicated distribution of the 

 heat than in the case of longitudinal tones. In producing the 

 tones it is best to use a tuning-fork, and to connect with one leg 

 the body to be investigated in the form of wire or thin tubes, in 

 such a manner that it constitutes the prolongation of the leg in 

 question. It was thus possible to demonstrate an increase of 

 temperature after sounding in the case of caoutchouc, lead, brass, 

 copper, iron, and steel ; and the intensity in the various materials 

 corresponded to the values obtained by longitudinal vibrations. 

 Yet in the loops in transverse vibrations there is, after sounding, 

 in general as great an elevation of temperature as on the nodes ; 

 in the case of caoutchouc it was certainly ascertained to be greater; 

 only at the free end it was in all cases null. The latter circum- 

 stance leads to an explanation of the phenomena. In transverse 

 vibrations the positions of greatest bending are those which nearly 

 coincide with the loops, and they are also places where most heat 

 is developed — just as in longitudinal vibrations the places where 

 there is the greatest change in density, which coincide with the 

 nodes, have also been seen to be places where most heat is deve- 

 loped. In like manner, in accordance with Kundt's experiments*, 

 the action of sounding bars on transmitted polarized light dimi- 

 nishes in the case of longitudinal vibrations towards the loops, 

 and in the case of transverse vibrations towards the nodes and 

 the free ends. 



Hence we may sum up the result of this investigation by say- 

 ing that every solid becomes perceptibly heated by being sounded, 

 provided that sufficiently powerful condensations and rarefactions 



* Poggendorff' s Annalen, vol. cxxiii. 



