232

PlateXXXIII.fig- 4-

Of Winds and Sounds,

founding Body, The utmost Limitsaudible Sounds are about 180 or 200 Mies.

<civ>

III. M

(CIV) 1. Let ABC represent the sonorous Bod/*by the tremulous Motion of its Parts, it will agit at ®the Air contiguous to every Point as A, where it wiHbe condensed to a certain small Distance, and make UPulse or Wave of Air in the Manner as has been large-ly strewn (Annotation CII). The first Wave or P u *‘ ewill by its elastic Power in expanding itself produce aSecond, that a Third, and so on; till the imprestsMotion be diffused thro’ too large a Quantity of Air tabe any longer sensible.

2. The Quantity of'Motion produced by each Tre-mor of the sonorous Body, being communicated succy'lively to larger Portions of Air, the Part thereof whff"each Particle will acquire will constantly decreaseThis Decrement of the Motion will be as the Incre-ment of the Number of Particles, which is as the Su-perficies of the spherical Shell; and since all Supe* - 'fides are as the Squares of their Diameters or Semi-d ,a "meters, therefore the Force in the Particles of I' 1Wave or Shell at D is to that in the Particles of ^ e .Shell at F as.AF 2 to AD«s that is, the Force of S° u11decreases as the Squares of the Distances increase.

3. It is plain, the Distance to which Sounds rn a Jbe heard will be proportional to the Magnitude or I*Vtensity of the Stroke made on the tremulousemitting the Sound ; for the greater that Stroke is,greater will. be the Agitation of the Parts of the so p0 'sous Body, and of course the greater will be the Fo^with which they will strike the Particles of Air. Lartipthe greater Force is upon the Air, the more fironA 7will it he condensed and expanded ; hence the gr ea -will be the Stroke at any given Distance on the Drffof the Ear, and consequently the greater will be tfieDstance at which the Agitation of the Air will be felfi "

4. The Experiments are numerous bv which st c

^ r , 1.0 1 • , ,, J -r^-^nre 01

been found, that Sound is audible to the Dist ance

50,