524 Scientific Nnus.—-Accounti of Beds, 



and gravitation are two forces which aft at the fame time on the whole fyftem of the machine ; 

 that gravitation a£ls as if the whole mafs were united at its centre of gravit)', while the re- 

 fiftance a£ls as if the whole of this mafs was united at another centre little diftant from the 

 centre of gravity of the cloth which forms the parachute, and very different from the former. 

 The parachute may be confidered as fufpendcd in the air by this centre of refiftancc. 



If the centre of gravity be not vertically beneath the centre of refiftance when the para- 

 chute is properly placed, it is evident (fays he) that it will incline to one fide, defcend ob- 

 liquely, ofcillate, and the fmalleft irregularity in its figure will caufe it to turn round its 

 vertical axis. It is alfo important that thefc two centres Ihould be at a diftance from each 

 other, fince the ofcillations will more readily take place the nearer they are. If they were 

 coincident, there would be no caufe why the whole apparatus (hould not overfet. C. Say 

 therefore propofes that the car or part of the ballafl fhould be fufpended at a confiderablc 

 diftance below the parachute. 



ACCOUNTS OF BOOKS. 

 Recherches experimentales fur le Principe de la Communication laterale du Mouvcment 

 dans les Fluides, applique a I'Explication de difFerens Phcnomenes hydrauliques. Par 

 le Citoyen J. B. Venturi, Profefleur de Phyfique e.\perimentale a Modcne, Membre dc 

 la Socicte Italienne, &c. i'c. A Paris, chez Houel & Ducros, Rue du Bacq, No. 940 — 

 Theophile Barrois, Rue Hautc-feuille, No. 22. Ann. VI. 1797.—, — Or, Experimental 

 Refearches concerning the Principle of the lateral Communication of Motion in Fluids, 

 applied to the Explanation of various Hydraulic Phenomena. By Citizen J. B. Venturi, 

 Profcflbr of Experimental Philofophy at Modena, &c. &c. 



I HAVE been favoured with a copy of this curious and interefting work by the learned 

 Profeflbr, which I have read with much pleafure. The commilFion nominated for that pur- 

 pofe by the National Inftitute of France have given a very corre£t analyfis, which I fhall 

 chiefly follow in my account. 



Citizen Venturi has introduced an horizontal current of water into a veflel filled with 

 the fame fluid at reft. This ftream entering the veflel with a certain velocity, pafles through 

 a portion of the fluid, and is then received in an inclined channel, the bottom of which 

 gradually rifes, until it paflTes over the border or rim of the veflel itfelf. The efFe£t is found 

 to be, not only that the ftream itfelf pafles out of the veflel through the channel, but 

 carries along with it the fluid contained in the veflel ; fo that after a (hort time no more of 

 the fluid remains than was originally below the aperture at which the ftream enters. This 

 fa£l is adopted as a principle or primitive phenomenon by the author, under the denomination 

 of the lateral communication of motion in fluids, and to this he refers many important 

 hydraulic fafls. He does not undertake to give an explanation of this principle, but (hews, 

 p. 37, that the mutual attra£lion of the particles of water is far from being a fuflicient caufe 

 to account for it. 



The firft phenomenon which the author propofes to explain by this eftablilhed principle is 

 the emilEon of a fluid through diflerent adjutages applied to the refervoir which contains it. 

 It is known that the vein of fluid which iflues from an orifice or perforation through a thin 

 plate, becomes contratled, fo as to exhibit a fe£lion equal to about 0,64 of the orifice itfelf, 

 fuppofcdto be circular; and that the plact of tlie grcatcft contradion is ufuaily at the dif- 

 tance 



