gQ CASE OF SPOUTING FLUIDS. 



authority of Venturi on the other, made it defirable that the 

 experiment (hould be repeated ; and an apparatus Fig. III. 

 Plate I. was conftruded, in the houfe of the Royal Inftitution, 

 for performing it in a fimple and fatisfadory manner. The 

 ciflern employed was a cube of nine inches : clofe to the 

 bottom a cylindrical tube was inferted, in a horizontal direc- 

 tion, nine inches in length, and half an inch in diameter ; an- 

 other tube, of exactly the fame dimenfions, was provided with 

 a flat funnel at its upper end, and its lower end was fitted to 

 Aide in a collar placed in one of the upper angels of the ciflern. 

 Experiment fo that it was fupported in a vertical pofition. Water was 

 poured into the funnel, as fafl: as it could be tranfmitted through 

 the tube, and, as the furface of the fluid rofe in the ciflern, the 

 vertical tube was drawn up, fothat its lower orifice was barely 

 immerfed in the water. It was expected, that if the velocity 

 of the water in the vertical tube were equal to the velocity 

 correfponding to half its length, the water in the ciflern would 

 fland at the height of four inches and a half, or one half of 

 that length, and that the prefl'ure of this head of water would 

 generate, in the water flowing tiirough the horizontal tube, 

 nearly the fame velocity as the column of water would acquire 

 in its defcent through the vertical tube : the fridlion and 

 refiflance being in both cafes the fame, 

 ftewed the con- But the refult was far different, and it fully Confirmed th6' 

 ^^^'^y' truth of the received theory : for the water rofe in the ciflern 



to the height of eig[)t inches, which was very nearly the length 

 of the tube. It is true that the water had already fome velocity 

 when it entered the funnel ; but nioft of this mufl have been 

 loft by reflection from its fides and bottom ; and the quantity 

 of air bubbles, that were unavoidably carried down with the 

 water, mufl have fully compenfated the little that remained. 

 The entire ad- ^^ appears therefore, that we are to confider this effedl in a 

 heting column in light fomewhat different from that in which it was placed in 

 th^at" o/ here" ^^^ '^'^^"^*^^ °" hydraulics. The water acquires all its velocity, 

 aftive upon the in confequence of the prefigure of the atmofphere a6ting jointly 

 furface of the ^-^^^ j^^ cohefion, in a very fmall fpace at the entrance of the 



fluid, and pro- . i i ■ . i i 



duces the fame tube : conlequently, durnig the whole time of its defcent it 



efteft asanheadg^^yj^gj. ,iq ,iew motion, and the whole force of its gravitation 



mufl therefore be at liberty to a€t in any other way ; hence the 



whole column produces the fame degree of prefliire as if it 



were at reft, and caufes the atmofphere to prefs on the water 



above 



