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Discharge of Liquids through Conical Ajutages. [Book V.

drical one to the conical frustrum C D. Supposing the diameter of Cto be unity or 1, that of D should be 1.8, and the distance between them9. The increased discharge ceases when the tylindrical part of the tubeB C is of considerable length, and of the same bore as the smaller endof C D.

A tube of the form represented at No. 202 was applied by Venturi tothe same reservoir, the depth of water in which was also kept at 32Jinches. Three glass tubes, ABC, were connected to the under side ofthe pipe, and their lower ends inserted into a vessel containing mercury.When water flowed through the pipe the mercury rose 53 lines in A, 20in B, and 7 in C. These quantities correspond with 62 inches of waterin A, 24 inches in B, and 8 in C. The length of the pipe should not ex-ceed four times the diameter of its smaller end, and its sides should notdiverge from each other more than what is required to form an angle offrom three to four degrees. By this principle it will be perceived, thatwater may also be raised from a lower level and discharged at an upperone, and in many situations it might doubtless be adopted with advantage.See Nicholson’s Journal, vol. ii, and Hachette’s Traite Elementaire desMachines.

Different causes have been assigned for the increased discharge ofliquids through conical tubes. One is certainly to be found in the materialof which they are made ; for when formed of or lined with any substancethat repels or refuses to coalesce or be wetted with the effluent water, aswax, tallow, &c. the effect ceases. The phenomenon therefore dependsupon the attraction and adhesion of the liquid to the sides of the tubes,which sides exert a capillary force in drawing the particles of the liquidtowards them, so as not only to prevent its assuming the figure of the con-tracted vein when entering the tube No. 202, but also drawing the particlesto the diverging sides of the discharging ajutage.

A knowledge of the increased discharge of liquids from conical tubeshas led some persons to take advantage of the fact, to the serious injuryof others. We have heard of the purchaser of a water power, who ac-cording to the covenant was to connect his mill-race with the dam by atrunk of a certain specified bore at the junction. This he did, but makingthe sides of the trunk diverge as in the last figure, the proprietor ofthe dam was astounded to find the water, as if moved by instinct, givingthe new channel the preference, and unaccountably persisting in rushingthrough it with a velocity that threatened to drain the well supplied reser-voir, and leave his own mill to take its rest. This increased discharge isnot confined to tubes of a cylindrical or conical form. The walls of thechannel may be straight, and its section may be a square, a triangle, &c.as well as a cirele.

There is some reason for believing that overreaching in this way is notwholly a modern discovery. No city, ancient or modern, was perhapsever supplied with water in greater profusion than old Rome ; yet the eon-tents of her aqueducts were meted out with ecönomy, and, as in moderntimes, a revenue was derived from the sale of the water. The superin-tendence of the aqueducts and of the distribution of the liquid through thestreets and houses were always intrusted to a citizen of rank and talents.The celebrated Frontinus held the office under Nerva, by whose directionshe wrote two books on the water-works of Rome , the times of their erec-tion, districts of the city supplied by each, the number of public and pri-vate f'ountains, quantities of water discharged from different sized orifices,&c. From him we learn that numerous frauds were practiced in obtainingmore than the assigned quantity of the liquid, one of the means for pre-