Tubes rendered harmonious ly Hydrogen Gas. if 



than others. The fize of the bulb appears lo me alfo to con- 

 tribute towards the fame effeift. The found will be perma- 

 nent for fome moments; it will then gradually decreale, and 

 at length will entirely ceafe. By fuffering the apparatus to 

 cool, 'and taking care to make the liquid condenfed along 

 the fides of the tube todefcend into the bulb, the experiment 

 may be repeated as often as may be thought proper. 



Such is the experiment by means of which, in my opi- 

 nion, the phcenomenon of the harmonious tubes may be ex- 

 plained in a fatisfaftory manner. Let us now examine what 

 takes place in tubes with a bulb, and what are the eflential 

 conditions necellary to make them emit a found, and let us 

 endeavour to difcover the caufe of this found. We (hall then 

 compare them with the tubes employed with hydrogen gas, 

 and (hall examine in what thefe two inftruments refcmble 

 each other in the effects they produce, the diflerences they 

 exhibit under the fame relations, and the caufes of thcfe dif- 

 ferences. 



The efll-ntial conditions neceffary to make tubes with a 

 bulb refound are: i(l, That the veffel has a bulb : I was 

 never able to excite fonorous vibrations in a tube fimply 

 clofed at one of its extremities. 2d, This bulb muft con- 

 tain an evaporable liquid : water fucceeds ver^r well ; but it is 

 attended with the dil'advantage of forming in the tube, whca 

 it pafTes from the ftate of vapour to the liquid Rate, a fmall 

 drop which often obftrufts it entirely, and, ibmetimes, falling 

 on the heated part of the glafs, occalions a rupture. Mercury 

 is not attended with the fame defe6t : I was never able to pro- 

 duce founds with ether, fpirit of wine, or concentrated ful- 

 phuric acid. The quantity of liquid contained in the bulb 

 IS not a matter of indilTercnce ; it muft be as fmall as poffi- 

 ble : if there be too much, the tube becomes filled with va- 

 pours, which completely expel the air from it, and, heating it 

 every whore in an uniform manner, it no longer emits any 

 found. The third eflential condition is the application of a 

 ftrong heat to the bulb while the reft of the tube remains 

 cold ; for, if there be not a very ftriking difference of tempe- 

 rature between the bulb and the tube, there will be no fonorous 

 effcft. In the laft place, the prefencc of atmofpheric air 

 is indifpciifably necefl'ary : if it be entirely expelled, no efl'eft 

 can be produced. In all the periods of the experiment it 

 will be found that the vapour lllls only a certain portion of 

 the inftriunenl, and that it always contains air. I niade 

 federal trials to deterniine exactly the fpacc occupied by the 

 vapour at the moment ulun the found is heard; and I have 

 found ihatj iu faiull lubes al Icallj this fpacc is fonK\vJ)at Ids 



lliau 



