270 ON THE velocitV of air 



The atmofphere which in this cafe will make no difference) equal to 33 muUi- 



preijes equal to Iied fa g4Q QJ . 2?72() feefc thfe aJ . th f rQot f J g • £ 



3 3 feet of water, r . ' ' ~ 



or 27720 feet of 32, the velocity at the depth, fo is the fqiiare root of 27720 to 

 air. It would j 332 feet per fecond, the initial velocity df the atmofphefe iri- 



therefore propel l J * 



air into a va- lo a vacuum. 



cuum with the To prove whether air cdmprefled by 33 feet of water wduld 

 thisfaU: viz. De impelled into the atmofphere with the above velocity, I 

 ^/i6 ^27720 have made, amongft many more, the following experi- 

 :: 32 feet: 1332 ments . 

 feet per fecond. • . ^ j,. ^ r i ' ' « J 



Experiments. A> plate xiv. fig. 1 *> is a veflel of a known capacity, into 



Air is cdmpief. ^he top of which is fcrewed an aperture of a known area. 



by a known The tube 7V/, recurve at d, is foldered or fcrewed into the 



height of water : top of the faid veffel. The hole a is flopped, and water poured 



into the tube at T till it is full, at which time a quantity of 



water will have palled out of the tube ate?, and condenfed the 



air in the veflelj more or lefs as the tube T d is longer or 



fhorter. 



and fuffered to At this time a perfon who has clofed the aperture at a with 



iflue through an a fi n g er f one hand, and held a half fecond pendulum in the 



known dimen- other, removes both at the fame time, while at the fame mo- 



fions. Its ve- me nt an atfiftant opens a cock over the tube T, which fupplies 



fron?the quan" ** w * tn water as ^ as ^ can defcend into A. The moment 

 tity and the that the water appears at a, the time-piece is flopped, and the 

 time of expelling the air is noted, from which, by knowing the 

 capacity of the veflel, the velocity may be obtained. 



If the tube Td fliould be continued near the bottom of the 

 veflel A while it was filling with water, the length of the com- 

 pelling column would be gradually diminifhing, and of confe* 

 quence the preflure would be conftantly changing; hence the 

 open end of the tube is as near the top of the veflel as is confif- 

 tent with a free paflage for the water. 



EXPERIMENTS. 



The veflel A contained 15 lb. 6 oz. of water, from which we 

 find its capacity is 425.088 cubic inches. 



The area of the aperture a, through which the air is expelled, 

 .0046 inches. 



* There being no figure in the Tranfa&ions, I have inferted the 

 drawing referred to. N, 



Exper t 



