»30

jyisnharging Water above its Source by Siphons. [Book V.

sents two atmospheric pumps placed one above the other, and the lowestone raised it from “24 to 30 feet,” and the upper one “ may raise it fromthence 24 or 30 feet” higher. The “ Forcible Movements,” it will beremembered, was published about thirty years before the discovery ofatmospheric pressure.

Contrivances for discharging water from the highest part of siphonshave often been proposed. They are to be met with in several old authors,and the principle of most of them may be found in the Spiritalia. Theyare however seldom employed, because circumstances on which they de-pend rarely occur ; and other devices are preferable even under thosecircumstances. A descriptive account of a few of them may interest somemachinists, and be serviceable to others, viz : by preventing them fromexpending their energies in devising similar things. Indeed in this respectbooks which contain accounts only of the best machines are not always themost useful to inventors. In whatever department of the arts these menexercise their talents they are almost certain to fall at one time or anotheron old devices, which appear to them both new and equal to similar plansin common use. Books therefore which describe rejected and antiquatedcontrivances are not so worthless as some persons imagine.

One plan to raise water by a siphon consists in enlarging or swelling itout at or near the bend, or what amounts to the same thing, connectingthe legs to an air-tight vessel; and when this becomes filled the commu-nication between it and the legs is cut off by valves or cocks, and thecontents drawn off. When this is done the vessel remains filled with air,which if admitted into the legs would stop the action of the siphon. Itmust therefore, in Order to expel the air, be filled with some liquid toreplace that drawn out. Suppose a siphon of this kind be designed toraise water for the supply of a dwelling, in or near which the vessel isplaced, it may then be refilled with refuse or impure water, which onadjusting the cocks will pass down the discharging leg. Then after-ashort time elapses, the vessel will again be filled with fresh water, whichmay be again exchanged for the same quantity of impure.

In locations where river, salt, or any other water can thus be exchangedfor fresh, and it is desirable to do so, such devices are applicable. (Inhreweries, distilleries, &c. the descent of one liquid may thus be made toraise another.) It should however be observed that an equal quantity must,be given for that received, and it must descend rather more than the latterrises. But when circumstances allow these conditions to be fulfilled, theapparatus is not always to be depended upon ; air insinuates itself throughthe minutest imperfections in the pipes and cocks, and often deranges thewhole. One of these siphons is described in Nicholson’s Journal, 4to.vol. iv, and in vol. ii, of Gregory’s Mechanics. Another in the Biblio-theque Phisico-Economique, which is copied in vol. x, of the Repertoryof Ärts, 2d series. Another is figured in Art and Nature, A. D. 1633,with two close reservoirs at the top ; and Porta, in cap. 3, book xix, of hisMagic, describes another, with the close vessel on the top of a tower : thedischarging leg is described as terminating in another close vessel of thesame size as the one above, and furnished with a cock and funnel throughwhich to fill it, and another cock to discharge the contents : this charg-ing vessel from his description appears to have been placed on the grounda little below the spring and then emptied—if so, the apparatus could notact. He does not appear to have been aware of the necessity of the con-tents of the lower vessel being discharged from the orifice of a pipe asmuch below as the receiving vessel on the tower was above the spring.The device (which he probably imperfeetly copied from some older author)