ij6 Experiments en the lateral Communication of Motion In Flulas, 



I repeated this experiment with the compound tube fig. 5, and the refults were the 

 fame. 



Experiment 7. The cylindrical pipe K L V, fig. 6, was applied in an afcending and nearly 

 vertical fituation to the orifice R, fig. 8, of the veflel H I, of which the end H Communicated 

 by an opening of confiderable extent with the water of the refervoirX, fig. i. The charge on. 

 the upper extremity V of the tube was 27,5 inches. I inclined the tube a little from the 

 vertical direction, in order that the jet might not fall back upon itfelf. The glafs tube Q_RT, 

 fig. 6, in this new fituation was fo difpofed that its lower extremity was immerfed as before 

 in the coloured liquid of the veflel T. When the efflux was permitted, the expenditure of 

 four cubic feet was made in 34 feconds ; and the coloured liquid rofe in the tube R T to the 

 height of near 20 inches. With the dmt charge of 27,5 "inches the orifice of 18 lines 

 in a thin plate would have afforded the four cubic feet in 4.5 feconds. 



Experiment 8. A cylindrical vefiel of 4,5 inches diameter had in its vertical fides near 

 the bafe a circular opening of 4,5 lines in diameter, opened in a tliin phte of tinned iron. 

 The furface of the water contained in this vefTel was 8,j inches above the centre of the 

 aperture. The water was then fufFcred to flow out of this aperture in the thin plate, and its 

 furface was deprefled feven inches in the velTel in 27,5 feconds of time. 



To the fame aperture was applied a cylindric tube of the fame diameter, and in length 

 1 1 lines. The veflel was filled to the fame height,as before, and, the water bemg fuff«red to 

 flow out, its furface was depreffed feven inches in 21 ftconds. 



The fame experiment was iifterwards repeated in the receiver of the air-pump, under 

 which the mercurial gauge flood at no more than JO lines in height. The furface of the 

 water in the vefl"el was depreflTed feven inches in 27,5 feconds, whether the aperture was 

 made in a thin plate, or whether it was provided with an additional cylindric tube. 



The height of the coloured water in the tube of glafs meafures the adtive quantity oTthe 

 preflure of the atmofphere, which is exprted on the furface of the water to increafe the ex- 

 penditure. For example, in the fixth experiment 32,5 + 24 inches charge on the orifice 

 P, and we have nearly \/j2,5 : ^56, 5 : : 31": 41'', as is required by the Common theory 

 of the motion of fluids which ifTue out of veflcls by a fmall aperture. The fame obtains in 

 Experiment 7. 



Daniel Bernoulli made the 7th experiment in defcending tubes, and in diverging conical 

 tubes, and evplained the refult merely by the theory of confervation of living forces. Kuler 

 and d'Alembert obferved to him, that the preflure of the atmofphere was concerned in the 

 efFe£l*. Though the cafe of the defcending rube be different from that of the horizontal or 

 afcending tube, the knowledge of the firfl of thefe two cafes may neverthelefs facilitate the 

 knowledge of the fecond. Befides which, the caufes which a<ft in both cafes are often com- 

 bined together, and it is neceflary to be well acquainted with both, in order to diftinguifli the 

 refult?. On this account it is, that in the following propofition I have turned from my prin- 

 cipal fubjedl for a moment to confider the firfl cafe, after which 1 fliall return to the (econd. 



Propofition 4. In defcending cylindrical tubes, the uppsjr ends of which poflefs the form of 

 the contraifted vein, the expence is fuch as correfponds with the height of the fluid above the 

 inferior extremity of the tube. 



* D'Alembert, Traite des Fluides, Art. 149. 



The 



