i,6 Tuhes rendered harmonious hy Hydrogen Gns, 



into which the air mflies to be repelled by the new vapfturs, 

 that contradl in their turn. Is it from this ahernate motion, 

 produced by the great expanfion and fubfeqiient contradion 

 cf the vapours, tliat the fonorous vibrations refidt* ? 



Such were the conjettnres which might be formed on the 

 probable caufe of this phasnonienon, when I accidentally 

 met with a faA w-hich apj^ared to me to give them fome 

 weight. 



I had a thermometer tube about a line in diameter, at the 

 extremity of which a fmall bulb was blown. In this bulb 

 was a drop of water, which I wUhcd to expel : for this pur- 

 pofe I expofed the bulb fcveral times to the flame of a fpirit- 

 of-wine lamp. I was agreeably furpriled to hear the tube 

 emit a harmonious found. 



To repeat this experiment with fuccefs, the tube employed 

 muft be from i to 2 or 3 lines in diameter : its length may 

 be about from 3 to 4 oi' 5 inches : it muft have blown at one 

 of its extremities a bulb the diameter of which is about triple 

 that of the lube. It is not necelfary that it ftould be regular. 

 It even appears that, if it were a little flatted, the found 

 emitted would be higher. Into this bulb introduce a little 

 quantity of water or mercury, and then expofe it to a ftrong 

 heat : that of a common fpirit-of-wine lamp will, in general, 

 be fuflicirnt; but the flame mull be large and lirong when 

 the operation is performed with a large tube. After the bulb 

 has been expofed for fome moments to the heat, it will emit 

 a found. Tubes of a large diameter produce a ibund lower 



■■* ft appears to me probable that the found produced by the air which 

 rufhes into the vacuum is more intenfe than that whxh refuhs from an 

 expanfive force. The dreadful noife occafioiied by tiie detonation of bub- 

 bles of hydrogen gas and oxygen is well known, and yet the lighteft ob-« 

 jefts which furround the veiiel are not even agitated by it; wher.ce we may 

 conclude that this phsenomenin is produced by the fudden vacuum refulr- 

 ing from the deftruftion of the gas. The detonation of an inflammable 

 gas piftol is much ftronger than that of the air-gun, though the effeft is 

 Jefs conliderahle ; probat-ly becaufe in the piftol a vacuum fuccecds the 

 firft expanfive force. Every body is acquainted with that children's play- 

 thing called the humming top. It conlifts of a hollow fphere with an 

 aperture at the circumference, which being made to turn rapidly on its 

 axis produces a very ftrong humming noile. Vv'hat is the caule of this 

 noife? The fame, in my opinion, as that above mentioned : the centri- 

 fugal force ex)iels t'l': air from the fphere through its a(itrture; a kind of 

 vacuum is' formed in it, the exterior air continually tends to enter it, and 

 is immediately repelled, and hence a fcries of ibnorous ofcillations, -^Thc 

 Author. 



The effe6t here fpoken of feems rather to arife from the velocity with 

 which the edge or lip of the oritice meets the <iir ; for the fame found may 

 be produced by direfting a ftream of air au;ainft the lip when the top is 

 ftationary . — Edit. 



7 than 



