ACOUSTICS. 



distance is seven times 1142 feet. In like 

 manner, if you observe the numhe* 

 conds between the ligbtnfaig and the iv- 

 portofthe thunder, yon know the distance 

 of tin- clour! from whence it proceeds. 

 Hut, accordingto another philosopher. Dr. 

 Thomas Viung, the velocity of sound is 

 not quite so ifi-cat. " It lias been demon- 

 M rated," he observes, "by M !) I ,;i 

 (Jrange and others. that any impr 

 u hatever,communicatedtoonc particle of 

 ic fluid, will he transmitted through 

 that fluid with an unifonn velociu, d'e- 

 pending on the constitution of the fluid, 

 without reference to any supposed laws 

 of the continuation of that impression. 

 Their theorem for ascertaining 1 this \elo- 

 city is the same as Newton lias deduced 

 from the hypothesis of a particular law of 

 continuation : but it must he com 

 that the result differs somewhat too wide- 

 ly from experiment to give us full con- 

 in the perfection of the theory. 

 Corrected by the experiments of various 

 rs. the velocity of any impression 

 by the common air i)i:a. at 

 :m average, lie reckoned 1130 feet in a 



I." I'hil. Trai,- Mil. \C. 

 Dr. D (rh am has proved by experiment, 

 that all sounds \\hatcvertrav--l at th 

 rate. The sound of a inn, and the strik- 

 ing of a hammer, are cquallv s \vift in their 

 motions ; tlir- softest whisper Hies us s\\ ift- 

 ly, as far as it goes, a the loudest thun- 

 der. To the e we may add, that smooth 

 and clear sounds proceed from bodies 

 homogeneous, and of an uniform 

 figure ; and harsh or obtuse sounds, from 

 such as are of a mixed matter and irregu- 

 lar figure. The velocitv of sounds is to 

 that of a brisk wind as fif-y to one. The 

 strength of sounds is greatest in cold and 

 air, and least in that which is warm 

 and rarefied. F,ver\ point against, which 

 the pulses of sound strike, b. 

 t re, from which a ne\\- series of pulseare 

 propagated in every direction. Sound 

 describes equal spaces in equal times. 



Then- is p-obahly no substance which 

 is not in some measure a conductor of 

 sound; hut sound is much enfeebled by 

 passing from one medium to another, if 

 a man, stopping one of his ears with his 

 linger, stops the othci 



it the end i>t 

 l-e applied tothe < 



erof a piece f timber, be it cversolong, 

 the beating of the watch will be distinctly 

 heard ; whereas, in the usual wa\ 

 scarcely be heard at the distance of 15 or 

 IS feet. The same effect will take place 

 ifh* stops both his ears with hi 



and restshis teeth, his temple, or thccar- 

 i-t of one of his . : rs. against 

 the siiek |i,-- , | ,,f ., 

 a gentle scratch may be made at on-- end 

 of a pole or rod, and the person \\hokeeps 

 the ear in close contact with the other 

 end of the pole will hear it very plainly 

 Thus, persons who are dull of 1> 

 may, by applying their 1 me part 



of an harpsichord, or ot ! i r body, 



hear the sound much better than other- 



Ifapcrsontie a poker or any ntherpiecc 

 of metal on to the middle of 

 nel about a yard long, V 

 thumbs or fingers the i 

 into his cars, wh;' 



against any obstacle, as an iron or stct 1 

 fender, he will hear a sound vcn like that 

 of a lar:<e ch.irch bell. 



Sound, like light, after it has been rc- 

 ntay be col- 

 : ''ii one point. a> into 

 it \\ill be there more audible 

 other part, even that at ih>- 

 whence it proceeded. On (I 

 i a whispering i^alh r\ 

 <(! The fonu of a whispering ! 

 must be that of :i > 



\lir, . ics. tig. 2. -, andifalov, 



sound or hisper be uttered at A. 

 orations expanding themseh 

 will impinge on the points 1), 1), D, &.c. 

 and (Vom thence be reflected to E, E, K, 

 and from thence to the points Kami G, till 

 at l:ist they all meet in < ', \\ b 

 will be the most dist-i ' The 



ntation of 90lind, by meansofspt :i! . 

 ing-trumpets, is usually illustrated 

 following' ma vnr.fig. .> be the 



tube, HI) the a\is, and 1{ tin- mouth-piece 

 forconveyingthe voice to the tube. Then 



idem, when a person speak ' 

 the trumpet, the whole force of i. 



is spent upon the . 



which will 1 i whole 



length, and, by various reflect :ionsfroi!i tin- 

 side ofthe tulte to the M\is, the air along 

 the middle part of the tube will he great 1\ 

 condensed, and its momentum propo;- 

 tionabh ihcreased. so that wlun it comes 



-.itethe air.it tile orifice of' he ti 



AC, its fon-e will be as much greaterthaii 

 what it would ha\ e been \\ itho'it tlu t 



.ill-face of a sphere, \\hose radius 

 is equal tothe leiit;tli of tlu 



;i th<- surface ofthe si-gment of such 

 spin-re, whose base is the orifice of the 

 lube. Fora pei-son speak iiu;.,t I?, with- 

 out the tube, u'ill n-.r. . of his 



I > I I I - S 



etube 

 Tthan \ 

 \ 



