1164 THEORY AND PRACTICE OF ENGINEERING. Book II.

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Fig. 1763.

SECTION OP SIPHON AND SUCTION BAM.

occupied by the bed and reservoir of air; the contrary takes place in the great ram siphon,such as that established at Marly ; the effect of the ram’s return has a tendency to intro-duce air through the joints of the tubes or cistern, and, as the junction cannot be per-fectly exact, this air enters in so great a quantity that the whole force of the ram is requiredto compress it.

In the first trials Montgolfier made with this machine he placed the ascension valve inthe interior of the ascension tube, at some distance from the body of the ram, and filledthe ascension tube with water, to put the ram more easily into motion; the atmosphericair, however, retained between the ascension valve and the column of water in the body ofthe ram, occupied so considerable a volume, as to destroy the useful effect of the ram, theactive column being employed to compress this air : an inconvenience of this sort presenteditself when the siphon ram at Marly was experimented on.

Great Siphon for drawing off Hater , as employed at Metz in repairing a dyke constructedon the Moselle : it raised the water from the head of the dyke, and discharged it into the

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Fig. 1764.

CHEAT SIPHON LMPLOYED AT METZ.