ON THE SONIFEROUS VIBRATIONS OF THE GASSES. iSS 



liqnid that falls through the cock, and prevent its injuring the 

 bellows. 



Every time, before the receiver was exhausted, the wooden 

 pipe was carefully tuned to 0-2250 of a monochord or sonometer, 

 divided decimally, the monochord being tuned accurately to a Monochord. 

 C fork. The box of this monochord is made of straight-grain- 

 ed deal, and is 36 inches long, three inches wide, and 2 5 deep. 

 Over two immovable bridges, placed 30 inches asunder, a steel Its wlr«, 

 wire, 0017 of an inch in diameter, is strained by two endless 

 screws, placed at the extremities of the box, which act like the 

 screws of a modern English guitar. A long wire is preferable to a 

 short one, because a small alteration of the tension or tempera- 

 ture will cause a less perceptible difference in the pitch of the 

 sound it produces. Lord Stanhope used steel wire on his cu- Should be of 

 rious monochord, finding that it did not keep continually 

 lengthening, as brass or iron wires do when the tension is con- 

 siderable. A curious experiment is related of the Stanhope 

 monochord, which I have never yet seen explained. Two 

 equal wires were put on it, and brought in unison with G, an 

 octave below the treble clilf. One of the wires was then 

 shortened as little as the eighteen-thousandth part of an inch, 

 and this was said to produce invariably an audible healing, Beats. 

 which could be very sensibly felt with the finger as well as 

 heard ! What was the cause of this beating ? The length of 

 the G wire was 20 inches, which could be divided by that in- 

 strument into 360000 equal parts, consequently the length of 

 the altered wire was 359999 of those parts. Now, the vibra- 

 tions of strings, which differ in length only, being in the in- 

 verse ratio of their lengths ; if we assume 180 as the number 

 of vibrations in l" of that G at Concert pitch, the shorter string 

 will make only 180 0005 vibrations in l", and consequently 

 not a single beat can be produced by such an imperfect unison 

 in half an hour* ! The beating that was produced, therefore, 

 remains unaccounted for, 



* Sauveur, Chladni, and Dr. T. Young, consider every Ui or C as a Concert pitch, 

 power of 2, taking the fundamental C for unity. At this pitch, middle 

 C makes 256 " acoustic vibrations" in 1": Sauveur's experiments, in 

 1700, give 244, Ealer and Marpurg attribute to the same C 2S6 and 

 250 in 1"; Cavallo gives 256-8; Smith 247 ; Sard 262; Robison 240; 

 Hawkins 238-6 ; and Farey 241-5. 



M 2 ' Doctor 



