Great Retardation of tliiids through irregular Pipes. 487 



Rome in the year 1629, and defcribed by Scheiner*, it deferves the more attention, efpe- 

 cially as the great halo on the prefent occafion, having its fouth-weftern limb elevated to the 

 height of 540°, and its nortli-eaftern deprefled to within 14° of the horizon, was in an ob- 

 fique pofition, not eafily reconciled with the theory of Huygens, which Iccms to require that 

 fuch circles fhould be equally elevated above the horizon all round. It aifo (hews tliat 

 Scheiner's original plan of the halo at Rome, which reprefented it as oblique, may have 

 been right, and that Huygens' corre£lion, whicli'make3 it parallel to the horizon, was pro- 

 hably an erroneous conjediure. 



lam, 



dear Sir James, 



your humble fervant, 



WILLIAM HALL. 



in. 



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, 

 Prof ejfor of Experimental Philofophy at Modena, Member of the Italian Society, of the Inflitute of 

 Bologna^ the Agrarian Society of Turin, (Sfc. 



(Continued fronn page 426, vol. II.) 



Experiment XXIII. Tlie two tubes a B C, D E F, fig. 14. Plate XXn. are 15 inches 

 long ; their diameter is 14,5 lines. The conical portions A, D^ have the form of the con- 

 traftion of the vein of fluid, and are applied to the orifice P, fig. i . Plate VIII. of the pre- 

 fent volume, which is 18 lines in diameter, with 32,5 inches depth, or charge of fuperin- 

 cumbent fluid. The elbows, or flexures, B C, E F, are made in the plane of the horizon. 

 Thefe two pipes are made of copper foldered with filver, and the workmanfhip carefully 

 executed. The curvature B C was drawn out, or bended, into the form of a quarter of a circle, 

 by filling the tube with melted lead, in order that it might preferve its diameter during the 

 ad): of bending. The elbow D E F is conftruded in a right angle. The expenditure through 

 thefe two tubes' was compared with that afforded through a right-lined cylindrical tube of 

 fimilar dimenfions, and in like circumftances. The four cubical feet of water flowed out of 

 the cylindrical tube in 45" j out of the curved tube A B C in 50" ; and out of the angular tube 

 D E F in 70". 



4. It is of importance that the tube B C, fig. 13. Plate VIII. Ihould be of an equal 

 diameter throughout. It is not enough that care be taken that there fliall be no contrac- 

 tion, it is alfo neceflary that it fliould not be enlarged at any part. For fuch enlarge- 

 ments have nearly the (iime bad effed in the expenditure as contraftions. The pipe A O, 

 fig. 12. affords a much lefs quantity of fluid with the dilatations D E, H I, than if it were 

 of a diameter equal to that at B throughout its whole length. The following experiment 



agrees with the tlieory. 



• Smith's Optics, vol. I. § 534. 



3 R 2 Experiment 



