Chap. 6.] Water conveyed over rising grounds by Siphons. 529

We have known siphons from a quarter to half a mile in length, andformed of leaden pipes only half an inch in the bore continue running fromnine to fifteen months without once stopping, although no air-vessels wereattached to them. In one case the pipe was 1200 feet in length, the orificeof the discharging leg was but five or six feet below that of the receivingone, and the highest part of the tube was from 12 to 15 feet above thesnrface of the spring.

An opinion is current with some writers, that the extreme elevation towhich water can be carried by siphons was unknown to the ancients, andthat Heron, the most celebrated writer of antiquity upon these Instru-ments, was not himself aware of its limitation to about 30 feet. It is notclear that Heron was thus ignorant; but if he were, it would only showthat in this department of the arts he was no practical man . That ancientplumbers and pump-makers, who prepared and laid large siphons wereaware of the limitation there can be no doubt, just as the same dass ofmechanics were in modern times with regard to pumps, before philosopherswere informed of the fact or able to account for it. As however siphonsfor conveying water over hills and to great distances have always beenof rare occurrence, (comparatively speaking,) it is not at all surprising thateven some hydraulic engineers should have been thus ignorant with regardto them, although familiär with the extent to which water can be raised byatmospheric pumps. If some of these men have talked of conveyingwater by siphons over mountains, we never hear them speak of raising itto equal elevations through the suction pipes of pumps. Daily experiencein applying the latter to various depths prevented them from falling intothe error.

Baptist Porta, in the 19th Book of his Natural Magic, speaks of raisingwater by a siphon to the top of a high tower, and several old writers havethe same conceit. This was in accordance with the ancient doctrine of the•plenists, who denied the possibility of a vacuum. They attributed the ascentof liquids through siphons to nature’s abhorrence of a void, and imaginedthe elevation to be unlimited. But these men were philosophers, whosepractical knowledge was confined to portable experiments ; had they beenWorking pump-makers they would have known better ; they would havebecome advocates for the opposite doctrine— vacuists. So long was theerror of the plenists maintained, observes Switzer, “ that I have seen abook of Machines, written even in Queen Elizabeth’s time, by one Ward,an engineer, who ventur’d to give a sketch of a high hill, and a house at thebottom or side, over which, by a vast extended syphon, the water was tobe convey’d from one vale to another.” The author of the old treadse,entitled, ‘ Art and Nature,’ quoted at pp. 321, 375, was of the same opi-nion. “ How to convey water over a mountain : this experiment is as easieto be performed as any of the former, and indeed after the same manner,for you must Iay a pipe of lead over the mountain, with one end in thespring or water that you desire to convey, and the other end must liesomewhat lower; then open the pipe at the top of the mountain ; stopboth ends of the pipe, and with a tunnell fill the pipe full of water ; thenclose it up exactly that neither ayer nor water may come out thereat; thenunstop both the ends of the pipe, and the water will run continually,”(p. 10.) Decaus appears to have been better informed, if we may judgefrom his remarks respecting the perpendicular length of pipes of atmo-spheric pumps. In large engines, he recommends that they be not madeover 20 feet; and including the working cylinders, he says, “ I am ofopinion that it [the water] must not be constrained to rise more than thirtyfeet in height.” The second plate of his “ Forcible Movements” repre-