SOUND. 



have written concerning this fubjeft. Roberval gives it at 

 the rate of 560 feet in a fecond ; Galiendua, at 1473; Mer- 

 fenne, at 1474 ; Du Hamel, in the Hiftory of the Academy 

 of Sciences at Paris, at 1 172 ; the Academy del Cimento, 

 at 1 148; Boyle, at izoo; Roberts, at 1300; Walker, at 

 1338; fir Ifaac Newton, at 968; Dr. Derham, in whofe 

 meafure Mr. Flamfteed and Dr. Halley acquiefced, at 

 1 142. 



The reafon of which variety Dr. Derham afcribes partly 

 to fome of thofe gentlemen ufing llrings and plummets, in- 

 ftead of regular pendulums ; and partly to there not being 

 dillance enough between the fonorous body and the place of 

 obfervation ; and partly to there being no regard had to 

 the winds : Derham having found the effefts of the wind, 

 though not of any changes of weather. 



But by the accounts fince publKhed by M. Cafiini de 

 Thury, in the Memoirs of the Royal Academy of Sciences 

 at Paris for the year 1738, where cannon were fired at 

 various as well as great diilances, under great variety of 

 weather, wind, and other circumilances, and where the 

 meafures of the different places had been fettled with the 

 utmoil exaftnefs, found was propagated at a medium at the 

 rate only of 1038 French feet in a fecond. The French 

 foot exceeds the Enghfh by nearly feven lines and a half, 

 or is as 107 to 114; and confequently 1038 French feet 

 are equal to 1106 or 1 107 Engli(h feet. The difference, 

 therefore, of the meafures of Dr. Derham and M. Cafiini 

 is 34 French, or 36 Englidi feet, in a fecond. According 

 to this lad meafure, the velocity of found, when the wind 

 is ftill, is fettled at the rate of a mile, or 5280 Englifh feet 

 in 4t2oV. 



According to Mayer, the velocity of found in a fecond 

 IB 1 1 oj feet; according to Miiller, nog; and according 

 to Piftet, about 1180. According to Bianconi (C. Bon. 

 ji. i. 365.), in fummer, the thermometer being at 20°, 70 

 vibrations of the pendulum elapfed while a found paffed over 

 13 miles; in winter, 79 feconds, the thermometer being at 

 1.2°. In a cloud or mift, 155" elapfed while the found 

 paffed and repaiied. Hence the air (hould expand ^ for 

 21.2% or -j-^, for 1° of the thermometer employed, pro- 

 bably Reaumur's, which is ^i-^ for 1° of Fahrenheit. 

 The mean difference of the temperature of the air was 

 probably fomewhat lefs than is fuppofed, perhaps 17*^ 

 or 18°. 



Chladni infers, from the longitudinal vibrations of dif- 

 ferent fiibftances, a velocity of 7800 feet in a fecond in tin, 

 9300 in filver, 12,500 in copper, 17,500 in glafs and iron, 

 11,000 to 18,000 in wood, and 10,000 to 12,000 in to- 

 bacco-pipes. Thefe obfervations are fully confirmed from 

 different grounds. According to the elalticity of fir, as 

 inferred from an experiment of Mr. Leilie, the velocity of 

 an impulfe rtiould be 17,300. The velocity may be eafily 

 calculated from the found of a brafs-rod : if the number of 

 vibrations of the gravell found in a fecond be n, the velo- 

 city will be 978 — v", / being the length, and d the depth 



in feet. From an experiment of this kind, Dr. Young fays 

 (Left, on Phil. vol. ii. p. 266.) that he found tiie velocity 

 17,70c in crown glafs, and 1 1,800 in brafs. 



Some of tiie moll confiderable queries, relating to the 

 laws of founds, have been propofed by Dr. Dcrliam ; and 

 he anfwercd (cveral of them acciir;ittly, from e.speriments 

 made for that purpofo by himfelf, as follows : 



How far does a found move in a fecond of time ? Sound 

 moves 1 142 feet, or 380 yards m a fecond, which is juft an 

 Enghffi mile in 9^ or 9.25 half futonds ; two miles in 18^ ; 



Vol.. XXXIII. 



three miles, or a league, in 27!-, &c. ; and about 13 mile* 



in one minute. 



But fea-miles are to land-miles nearly as 7 to 6 ; and, 

 therefmc, found runs a fea-league in about 12 feconds of 

 time. It is a common obfervation, that perfons in good 

 health have about 75 pulfations, or beats, of the artery at 

 the wrill, in a minute ; confequently, in 75 pulfations, 

 found (lies about 13 land-miles, and about ii-j- fea-miles, 

 which is about one land-mile in fix pulfes, and about one 

 feamile in near feven pulfes, or a league in 20 pulfes. 

 And hence the diftance of objetts may be found, by know- 

 ing the time which found takes to move from thofe objefts 

 to an obferver; £g- upon feeing the flafh of a gun at fea, 

 if 56 beats of the pulle at the wrift were counted before the 

 report was heard, the dillance of that gun may be eafily 

 found by dividing 56 by 20, which gives 2.8 leagues, or 

 about eight miles. 



Does the report of a gun, difcharged with its mouth to- 

 wards us, come fooner than when the muzzle is from the 

 obferver ? By repeated experiments it appears, there ii no 

 difference m the found from this different direftion. 



Do founds move in the fame time, through the fame 

 fpaces, in all Hates of the atmofphere, and heights of the 

 barometer, by day and by night, in fummer and in winter, 

 in fnowy and in clear weather, in this or that climate ? By 

 repeated experiments, it does not appear there arifes any 

 difference from any of thefe different circumllances. 



Do the winds affect the motion of founds .' By repeated 

 experiments, it appears, there is fome, though a very fmall 

 difference, in the velocity of founds, with or againft the 

 wind ; which is alfo augmented or diminished by the ftrength 

 or weaknefs of the wind. 



Do a great and intenfe found, and a fmall or languid one, 

 move with the fame velocity ? It appears that they do. 



For by experiments, a cannon fired with a half-pound 

 charge of powder, was heard at about the diftance of 17^ 

 miles, in the fame time after the flafii was feen, as when 

 fired with a charge of fix pounds. 



Does the found of a gun move equally fwift at all elera- 

 tions of the gun ? It does. 



Do different quantities or llrengths of gunpowder oc- 

 cafion any difference as to the velocity of the found ? 

 None. 



Does found move in a right line the neareft way, or does 

 it fweep along the earth's furface ? And is there any dif- 

 ference in the time, if the piece be difcharged in an acclive 

 and a dcclivc pofition ? Sound moves the nearelt way ; and 

 the velocity appears to be the fame in accHvities as in de- 

 clivities. 



Have all kinds of founds, as thofe of guns, bells, &c. 

 the fame velocity ? And are founds equally fwift in the 

 beginning of their motion and in the end ? There appears 

 no inequality in either of thefe refpefts ; and, therefore, 

 the times in which found is heard are proportional to tl»e 

 diftance ; that is, at a double diftance it is heard in twice 

 the time, &c. 



SouNO, for the RefeBion, RefraSion, i^c. of. Sec £cud 

 and Puo.MCs. 



Sounds, /Irticulale. See Akticulate. 



Sound, in Mufic, denotes a quality in the fcveral agita> 

 tions of tlic air, confidered as their difpofition, meafure, S:c. 

 may make mufic or harmony. 



Mufical founds are moft frequently produced by the al- 

 ternate motions of fubftatices naturally capable of ifochro- 

 nous vibrations ; which (ubftaiiccs may be either folids or 

 fluids, or iiillruments compofcd of a combination of fluids 

 with folids. The rcfonance of a room or paffagc it 011c of 

 3D the 



