Pranob: FRANCISCI Baronis VERVLAM, Vicecomitisq S. ALBAN Printed for J. WALTHOE, D. MIDWINTER, W. INNYS, A. WARD, M.DCC.XL. UML 4783 . NATURAL HISTORY. CENT. I. Experiments in confort, touching the ftraining and paffing of bodies, one through another; which they call Percolation. D IG a pit upon the fea-fhore, fomewhat above the high-water mark, and fink 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 practifed upon the coaft of Barbary, where other fresh water is wanting. And Caefar knew this well when he was befieged in Alexandria: for by digging of pits in the feafhore, he did fruftrate the laborious works of the enemies, which had turned the fea-water upon the wells of Alexandria; and fo faved his army being then in defperation. But Caefar mistook the caufe, for he thought that all fea-fands had natural fprings of fresh water: but it is plain, that it is the fea-water; because the pit filled according to the measure of the tide and the fea-water paffing or ftraining through the fands, leaveth the faltness. 2. I remember to have read, that trial hath been made of falt-water paffed through earth, through ten veffels, one within another; and yet it hath not loft its faltness, as to become potable: but the fame man faith, that (by the relation of another) falt-water drained through twenty veffels, hath become fresh. This experiment feemeth to cross that other of pits, made by the fea-fide; 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 courfe of experiments, except they be led by great judgment, and fome good light of axioms. For firft, there is no fmall difference between a paffage of water through twenty fmall veffels, and through such a diftance, as between the low-water and high-water mark. Secondly, there is a great difference between earth and fand; for all earth hath in it a kind of nitrous falt, from which fand is more free; and befides, earth doth not ftrain the water fo finely, as fand doth. But there is a third point, that I fufpect as much or more than the other two; and that is, that in the experiment of tranfmiffion of the fea-water into the pits, the water riseth ; but in the experiment of tranfmiffion of the water through the veffels, 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: befides, I do fomewhat doubt, that the VOL. III, A very 161898 |