Experiments on the lateral Commtinkatkn of Motion in Fluids, I'j'i 



fheet of water conftantly flowed at Q^ At the inftant agreed upon, the paffages of the water 

 were again clofed, Every experiment was repeated fucceflively for a number of times, until 

 the agreement of the refults had removed every fufpicion of error. I am allured that even in 

 the mod: complicated cafes, the quantity of error could not exceed one fortieth part. 



The meafures indicated in the courfe of thefe experiments were taken from a toife adjuft- 

 ed by that of the Academy, which Citizen Lalaiide fent me in 1783. Thefe meafures, as 

 well as all the others of the i8th century, will undergo the fate which is prepared for them 

 by the eftablifhment of the new metre. They may be reduced to this new ftdndard, by ob- 

 ferving that the foot is to the metre as 100 to 308. 



The wifefl: philofophers have their doubts with regard to every abftraft theory concern- 

 ing the jr.otion of fluids ; and even the greateft geometers avow, that thefe methods, which 

 have afforded them fuch furprifing advances in the mechanics of folid bodies, do not afford 

 any conclufions with regard to ''i.'draulics but fuch' as are too general and uncertain for the 

 greater number of particular cafes. Imprefled with a conviction of this truth, I have attended 

 to theory only when ir combined with the facfts, and was iieceflary to unite them under a fingle 

 point of view. E.'cn this fmall portion of theory may, if the reader pleafes, be rejected) 

 and he may confider the following propofitions fimply as the refults of experiment. 



When I quote the eftimable work of Citizen BofTut, on hydrodynamics, I refer to the 

 edition of 1786*. 



Propofttion i. The motion of a fluid is communicated to the lateral parts which are at 

 reft. 



Newton has affirmed, that when motion is propagated in a fluid, and has arrived beyond 

 the aperture B C, fig. 2, the motion diverges from that opening, as from a centre, and is 

 propagated in right lines towards the latdVal parts N K, as well as towards S. The fimple 

 and immediate application of this theorem cannot be applied to a jet which iflues from the 

 aperture B C at the furface of rtill water. Circumftances enter into this cafe, which tranf- ' 

 form the refult of the principle into particular motions. It is neverthelefs true, that the jet 

 BC communicates its motion to the lateral parts N K; but it does not repel them towards 

 Pand Q_, but on the contrary tranfports them along with its own fleam towards S. 



Experiment \. The horizontal cylindric pipe AC, fig. 3, is introduced into the vefTel 

 DEFB, which is filled with water as high as DB. .Oppofite and at a fmall interval from 

 the aperture C commences a fmall reftangular channel of tinned iron, SMBR, which is 

 open at top S R ; the inclined bottom M B refts on the edge of the veffel B. It is 24 lines 

 broad; the diameter of the tube AC is 14,5 lines; the extremity A is applied to the 

 aperture P of fig. i. The water of the refervoir being fuffered to flow through the tube 

 AC, the jet rifes along the fmall channel MB, and flies out of the vefTel in the ftream B V, 

 By this means a current is produced in the fluid of the vefTel DEFB; this fluid enters into 

 the channel S R, and iflues by MBV along with the jet AC, fo that-in a few feconds the 

 water D B falls to M H. 



* I confider this treatife as fuperior to all which before were extant. It is founded on a combination of the 

 principles of experiment and of theory. I have prohted by thefe principles, and feveral particular remarks 

 which the fame Citizen BoiTut and Citizen Prony have been fQ good as to comm.utucate after perufal of my 

 memoir, V. 



Experimtnf 



