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Tumulus
Prænob: FRANCISCI Baronis VERVLAM, Vicecomitisq S. ALBAN

In Cancello Ecclefia S. Mich: apud S. ALBANVM.CO

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LONDON:
Printed for J. WALTHOE, D. MIDWINTER, W.INNYS, A. Ward,

D. BROWNE, C. Davis, J. and R. Tonson, and A. MILLAR.

M.DCC.XL.

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Experiments in confort, touching the straining and pafing of bodies, one through

another ; which they call Percolation.

D

and yet

IG a pit upon the sea-shore, somewhat above the high-water
mark, and sink it as deep as the low-water mark; and as the
tide cometh in, it will fill with water, fresh and potable.
This is commonly practised upon the coast of Barbary, where

other fresh water is wanting. And Caesar knew this well when he was besieged in Alexandria : for by digging of pits in the seashore, he did frustrate the laborious works of the enemies, which had turned the sea-water upon the wells of Alexandria ; and so faved his army being then in desperation. But Caefar mistook the cause, for he thought that all sea-Sands had natural springs of fresh water : but it is plain, that it is the sea-water ; because the pit filled according to the measure of the tide: and the sea-water passing or straining through the lands, leaveth the faltness.

2. I remember to have read, that trial hath been made of falt-water pafsed through earth, through ten vessels, one within another ; it hath not lost its faltness, as to become potable: but the same man faith, that (by the relation of another) falt-water drained through twenty vessels, hath become fresh. This experiment seemeth to cross that other of pits, made by the sea-side ; and yet but in part, if it be true, that twenty repetitions do the effect. But it is worth the note, how poor the imitations of nature are in common course of experiments, except they be led by great judgment, and some good light of axioms. For first, there is no small difference between a passage of water through twenty small vessels, and through such a distance, as between the low-water and high-water mark. Secondly, there is a great difference between earth and land; for all earth hath in iť a kind of nitrous falt, from which fand is more free ; and besides, earth doth not strain the water so finely, as fand doth. But there is a third point, that I suspect as much or more than the other two ; and that is, that in the

experiment of transmission of the sea-water into the pits, the water riseth ; but in the experiment of transmission of the water through the vessels, it falleth. Now certain it is, that the falter part of water (once falted throughout) goeth to the botom. And therefore no marvel, if the draining of water by descent, doth not make it fresh: besides, I do somewhat doubt, that the VOL. III. А

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