A continuation of new experiments physico-mechanical, touching the spring and weight of the air and their effects. The I. part whereto is annext a short discourse of the atmospheres of consistent bodies / written by way of letter to the right honourable the Lord Clifford and Dungarvan by the honourable Robert Boyle ...

EXPERIMENT XX.

Shewing that in Tubes open at both ends, when no fuga Vacui can be pretended, the weight of Water will raise Quick-silver no higher in slender than in larger Pipes.

BEcause I find it, even by Learned and very Late Writers, urg'd as a clear and cogent Argument against those that a∣scribe the Phaenomena of the Torricellian Experiment to the weight of the External Air; That tis impossible, that the Air, though 'twere granted to be a heavy Body, could sustain the Quick-silver at the same height in Tubes of very differing big∣ness, since the same Air cannot equally counterpoise Mercurial Cylinders of such unequal weights; and because this Objection is wont very much to puzzle those that are not well acquainted with the Hydrostaticks, I presume Your Lordship will allow me,

till I can shew you some Hydrostatical Papers, by which the Ob∣jection may appear to be but ill grounded upon the true Theo∣remes of that Art, to annex the Transcripts of a couple of Expe∣periments, (that I once made to remove this, supposedly insupe∣rable, Difficulty,) just as I find them registred in my Note∣books.

The I. Tryal. Sept. the 2. 1662.

We took a very large Glass-Tube, Hermetically seal'd at one end, and about two Foot and a half in Length. Into this we pou∣red Quick-silver to the height of 3 or 4 fingers. Then we took a couple of Cylindrical Pipes of very unequal sizes, (the wider being as big agen as the slenderer) and open at both Ends. The lower Ends of these two Pipes we thrust into the Quick-silver, and fasten'd them near their upper Ends to the Tube with strings, that they might not be lifted up, nor mov'd out of their posture, in which the convex Surface of the Mercury in both the Pipes seem'd to lie almost in a Level, the Tube also it self being plac'd upright in a Frame. This done, by the help of a Funnel we pou∣red in Water by degrees at the top of the Tube, and observ'd, that as the Water gravitated more and more upon the stagnant Mercury, so the included Mercury rose equally in both the Pipes, till the Tube being almost fill'd with Water, the Mercury ap∣peared to be impell'd up to and sustain'd at as great a height in the Big Tube, as in the Lesser, being in either raised about two In∣ches above the Surface of the Stagnant Quick-silver.

NB. 1. Having caus'd about half the Water (having no con∣veniency to withdraw any more) in the Tube to be suck'd out at the Top, we observ'd the Quick-silver in both the Tubes to sub∣side uniformly, and to reascend alike upon the reaffusion of the Water.

2. We endeavoured to try the Experiment (for their sake who have not the Conveniency to have such Tubes purposely

made) in a wooden vessel, into which, when it was fill'd with wa∣ter, we let down a flat Glass furnisht with stagnant Mercury, whereinto the Ends of the two Pipes were immers'd. But the Opaeousness of the Cylinder (which reduced us to see onely from the Top the Reflection of the stagnant Mercury,) and other Im∣pediments, disabled us to perceive the Motions and Stations of the Mercury in the Pipes, though we once made use of a Candle the better to discern them.

The II. Tryal.

We took a very wide Tube of Glass, of about a Foot long, and into it poured a convenient Quantity of Quick-silver. We took also two Pipes of about equal length, and of that disparity in Bigness that we newly mentioned, (those Pipes lately descri∣bed being indeed cut off from these we are now to speak of,) and these being fill'd with Quick-silver (after the manner of the Torri∣cellian Experiment) were by a certain Contrivance let down into the Tube, and unstopt under the Surface of the stagnant Mercu∣ry, and then the Quick-silver in the Pipes falling down to its wonted Station, and resting there, we poured into the Tube about a foot height (by Guess) of Water, whereupon the Quick-silver as it before stood, as it were, in a Level in both the Pipes, so it was, for ought appear'd to us, equally impell'd up beyond its wonted Station, and sustain'd there both in the slender and in the bigger Pipe, and upon the withdrawing of some of the Water it began to subside alike, as to sense, in them both, falling no lower in the bigger than in the slenderer. And Water being a second time poured down into the Tube, the Mercury did in both Pipes rise uniformly as before. By which and the former Experiment it sufficiently appeared, that a Gravitating Liquor as Air or Wa∣ter, may impell or keep up Mercury to the same height in Tubes that are of very differing Capacities: And that Liquors ballance each other according to their Altitude, and not barely according to their Weight. For in this last Experiment, the Additional Cylinder of one Inch of Mercury was manifestly rais'd and kept

up by the Water incumbent on the stagnant Mercury, (the o∣ther Cause, whatever it were, of the Mercury's Suspension, be∣ing able to sustain but a Cylinder shorter by an Inch.) And the same parcel of Water did counterpoise in the differing Pipes two Mercurial Cylinders, which though but of the same Altitude, (namely about an Inch) were of very unequal Weight.