BOOK VI.

201

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A— Sills. B—Pointed stakes. C—Cross-beams. D —Upright Planks.E —Hollows. F— Winds. G —Covering disc. H —Shafts. I —Machine

without a covering.

The second machine of this genus turns the blowing wind into a shaftthrough a long box-shaped conduit, which is made of as many lengths ofplanks, joined together, as the depth of the shaft requires ; the joints aresmeared with fat, glutinous clay moistened with water. The mouth of this con-duit either projects out of the shaft to a height of three or four feet, or it doesnot project; if it projects, it is shaped like a rectangular funnel, broader andwider at the top than the conduit itself, that it may the more easily gatherthe wind ; if it does not project, it is not broader than the conduit, butplanks are fixed to it away from the direction in which the wind is blowing,which catch the wind and force it into the conduit.

The third of this genus of machine is made of a pipe or pipes anda barrel. Above the uppermost pipe there is erected a wooden barrel, four