Tubes rcnJered harmonious hy Hydrog!n Gas. 2g 



of the tube take from it, at the moment of contaft, a portion 

 of the caloric, its volume dccreafes, at the fame inftant a 

 vacuum take-; place, and the air rcfumes its primitive fpace. 

 A new addition of caloric re(lore= to the vnpour its whole 

 elafticity, a part of which it fooii lofes in the fame manner. 

 This is a ronfequence of the ofrillatioiis of that nature which, 

 give to the air an undnlatorv movement. The undulations 

 reflefted by the fides of the tube become fonorous and ap- 

 preciable when they are ifochronous with the ofcillationS 

 produced by the caufe I have indicated. From fome tubes 

 it is impoflible to produce anv found : in thefe I am of opi- 

 nion that the reflcfted undulations cannot harmonize with 

 the primitive ofcillations, and that the one dellroy the other. 

 In tiibcs with bulbs, the found, after a certain time, becomes 

 weaker, and at length ceafcs. This may be explained by the 

 propagation of heat along the fides. When the bulb is very 

 warm, and the tube cold, the vapour which rifes from the 

 bulb fuddenly lofes apart of its volume, and the ofcillations 

 thus produced are (irong and frequent; but when the tube 

 has acquired a certain degree of heat, the vapour gradually 

 decreafes in volume by paffing from a very hot temperature 

 into a place lefs warm indeed, but which, however, has a 

 iufficient degree of heat to make the ofcillations, whi^h be- 

 come weaker and fainter, to ceafe at length entirely. That 

 fuch is the caufe of the ceilation of the found may be proved 

 hy applying a ftrong heat to the part of the tube already 

 heated, maintaining at the fame time the fame degree of 

 heat under the bulb : by thefe means the limits of the tem- 

 peratures are again very abrupt, and the found will be repro-. 

 duced in its full force. It may be readily conceived that the 

 fubftance of the tube mufl; be fome matter a non-conduclor 

 of heat : glafs, therefore, is preferable. • 



Let us now compare the apparatus of a tube having a bulb 

 with thofe tubes in which hydrogen gas is empToyed. In 

 the latter we have every thing neceflary for the produdion of 

 found, a vapour very hot, and confeqnently highly claitic ; 

 tor, as already obferv'ed, the place of the combuuion is at fo 

 hieh a temperature that the beak of tie glafs is conftantly 

 reel. This ht)t and elaftic vapour, at the moment of its pro- 

 dndlion, is in conlaft with the cold air, which enters the 

 tube at the bottom and iflues at the top ; its volume nnift 

 thrn dccrcafe a moment after it has touched that cold air; 

 new hot vapours fuccecd the former, and contraft in their 

 turn. This altcrnote cNpnnfion and conlrai'T^ion gives birth 

 to the unduhitory nioytment of the air^ and f<>norous uudula- 



t!0t)4. 



We 



