ON THE VELOCITY OF A I It. 2'79 



XI. 



Experiments on the Velocity of Air iJJ'uing out of a Vejfel in different 

 Circumjlances; teith the Defcription of an lnjlrumenl to meafure 

 the Force of the Blafi in Bellows, Syc. By Mr .Banks, Lecturer 

 in Natural Fhilofophy *. 



JL HE object of this inquiry may be announced in the fol- Propofitlon. To 



lowing; proportion: If an elaftic fluid is generated in a given determi | ie , tne 

 m i • ... .„. . mechanic tores 



veflel, or any way contained in it, and at liberty to mueout of the er reaction of aa 



laid veflel through a given aperture/ to determine the refi fiance ^ Ia . ftic Spouting 



which the veflel meets with from its action, or the power 



which it has of communicating motion to the veflel, as in a 



(ky-rocket, Sadler's fieam engine, &c. 



Before we proceed to relate the experiments, it may be All uniform 

 proper to premife certain principles deduced from theory. If ^ l ^^ ow f't 0m 

 a tube be filled with any kind of fluid, as air, ivater, mercury, the fame velocity 

 &c. and placed in a vacuum, every fluid will flow out with the* . v f f *^ lf the * 

 fame velocity. For though the preflure of a column of mer- however differ-' 

 cury of a given altitude be much greater than an equal column en c their denfi- 

 of water, yet the weight of the particles to be projected is 

 greater in the fame ratio. On the other hand, if air is lighter 

 than water, the particles projected are alfo lighter in propor- 

 tion. If a tube of 16 feet high be filled with air of any den- 

 fity, that air, like water, would flow into a vacuum with a 

 velocity of 32 feet per fecond, no corrections being made for 

 reflftancef. 



And if we take the gravity of air to water as 1 to 840, then Equal velocities 

 a column of one foot of water comprefling air, will produce as™ 111 be produced 

 great a velocity in that air as a column of air 840 feet high, ^^ by the 

 fuppofing it was of uniform denfity. preflure of an- 



If we take the whole preflure of the atmofphere equal tonight of the 

 53 feet of water, or its height (fuppofing it to be equally denfe, former to that 



of the latter, 

 » From the Manchefter Memoirs, Vol. V. p. 398. ^ JjJJJ 1 * 3 ' as 



T In the fuppofition of a perpendicular tube open at the top, filled 

 with air or any elaftic fluid, the author takes the denfity of the co- 

 lumn at the bottom, or where the aperture is made, to arife folely 

 from the weight of the elaftic column j and the altitude to be that 

 which would be if the whole column were reduced to the denfity of 

 that at the bottom. 



which 



