278
Hydrostatics.
pi. XIV,fig. 14'
From what has been premised of the Na-ture of Fluids, it will be easy to understand,
that
Bodies ; and when so much is got in as will make themspecifically heavier than the Water, then they will be-gin to descend one after another ; and by varying theDegree of Pressure you may keep them suspended inany Part of the Fluid as you please.
5. It is to be observed, that the Matter of which theBodies of those Images and Bubbles are made ought tobe specifically heavier than Water, that they may sinkwhen fill’d with Water, which otherwise they could notdo : They are therefore made with Glass, which isabout three Times heavier than Water. Also theHoles in the Feet ought to be very small, lest the Watershould run out in the Air.
6. On the contrary, if the Images were but just hea-vy enough to sink to the Bottom of the Jar, if then theBladder, instead of being prefs’d down, were lifted upfrom the Surface of the Water, the Air would expanditself, and have a less Spring ; and therefore the Airalso in their Bodies would exert its Spring, (whichis now greater than that under the Bladder) and drivesome Water out of their Bodies, by which Means theywill become specifically lighter than the Water, and risein it to the Top.
7. The Image or Bubble will sink or swim withoutthe Artifice of a Bladder, if nicely managed ; for ifCare be taken to have just so much Water in the I-mage as will render it but very little higher than theWater, it will then swim at the Surface ; if then youput it into a proper Depth, the natural Pressure of theFluid upwards will force so much Water more into it,as to make it heavier than Water, and from that Place itwill, of its own Accord, sink down to the Bottom.Whence it appears the same Body will sink or swim inthe same Medium, according to the difterent Circum-stances it is under from the Medium, and not from anyThing in itself.
8. If any Vessel AB be fill’d half full with Salt Wa-ter to C, and a Bubble at B be made just heavy enoughto sink therein to the Bottom ; and after that an I-
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