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68 Of Hydroßatics.

How a man Hence, if a man stands upon the upper board, and blows into thesei 7 ra wardb’^ e ^ 0ws through the pipe B, he will raise himself upward upon thehis breath. y board : and the fm aller the bore of the pipe is, the easier he will beable to raise himself. And then, by clapping his finger upon the topof the pipe, he can support himself as long as he pleases; provided thebellows be air-tight, so as not to lose what is blown into it.

This figure, I confess, ought to have been much larger than anyother upon the piate; but it was not thought of, until all the rest weredrawn: and it could not so properly corne into any other plate.Howleadmay Upon this principle of the upward pressure of fluids, a piece of leadswim inVa ma y mac ^ e t0 lUirt in water, by imrnerstng it to a proper depth,tei-. and keeping the water from getting above it. Let CD be a glass tube,

7 - open at both ends, and EFG a flat piece of lead, exactly fitted to thelower end of the tube, not to go within it, but for it to stand upon ;with a wet leather between the lead and tube to make dose work.Let this leaden bottom be half an inch thick, and held dose to thetube by pulling the packthread IHL upward at L with one band,whilst the tube is held in the other by the upper end C. In this situa-tion, let the tube be immerfed in water in the glass vessel AB, to thedepth of flx inches below the furface of the water at K ; and then,the leaden bottom EFG will be plunged to the depth of fomewhatmore than eleven times its own thicknefs: holding the tube at thatdepth, you may let go the thread at L ; and the lead will not fall fromthe tube, but will be kept to it by the upward pressure of the waterbelow it, occasioned by the height of the water at K above the levelof the lead. For as lead is 11.33 times as heavy as its bulk of water,and is in this experiment immerfed to a depth fomewhat more than11.33 times its thicknefs, and no water getting into the tube betweenit and the lead, the column of water EabcG below the lead is pressedupward against it by the water KDEGL all around the tube; whichwater being a little more than 11-33 ^lnes as high as the lead is thick, issufficient to balance and support the lead at the depth KE. If a littlewater be poured into the tube upon the lead, it will increafe theWeight upon the column of water under the lead, and cause the leadto fall from the tube to the bottom öf the glass vessel, where it willlie in the situatioh b d. Ör, if the tuhe be raifed a little in the water,the lead will fall by its own weight, which will then be too great forthe pressure of the vväter around the tube upon the column of waterbelow it.

Let two pieces of wood be plained quit flat, so äs no water mayget in between them when they are put together: let one of the

pieces,

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