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 XV.

About the greatest height to which Water can be rais'd by Attra∣ction or Sucking Pumps.

SInce the making and the writing of the foregoing Experiments, having met with an opportunity to borrow a place some∣what convenient to make a Tryal to what height Water may be rais'd by Pumping; I thought not fit to neglect it. For though both by the consideration of our Hypothesis, to whose truth so many Phaenomena bear witness; and though particularly by the Consequences deduceable from the three last recited Experiments I were kept from doubting what the event would be, yet I thought it worth while to make the Tryal.

I know what is said to have been the Complaint of some Pump-makers. But I confess the Phaenomenon, 'twas grounded on, seem'd not to me to be certainly enough deliver'd by a Wri∣ter or two, that mention what they complain'd of; and their ob∣servation seems not to have been made determinately or carefully enough for a matter of this moment. Since that which they com∣plain of seems to have been in general, that they could not by pumping raise Water to what height they please, as the common Opinion of Philosophers about Natures fuga vacui made them expect they might. And it may well have happen'd, that as they endeavoured onely to raise it to the height their occasions required, so all that their Disappointment manifested, was, that they could not raise it to that particular height: which did not de∣termine, whether if the Pump had been a Foot or a Yard shorter, the Water would then have been elevated to the upper part of it or no: but that which I chiefly consider is, that these being but Tradesmen, that did not work according to the Dictates of, or with design to satisfie, a Philosophical Curiosity, we may justly suspect, that their Pumps were not sufficiently stanch, nor the O∣peration Critically enough perform'd and taken notice of.

Wherefore, partly because a Tryal of such moment seem'd not to have yet been duely made by any; and partly because the va∣rying weight of the Atmosphere was not (that appears) known, nor (consequently) taken into consideration by the ingenious Monsieur Paschal in his famous Experiment, which yet is but a∣nalogous to this; and partly because some very Late as well as Learned Writers have not acquiesc'd in his Experiment, but do adhere to the old Doctrine of the Schools, which would have Water raiseable in Pumps to any height, ob fugam vacut, (as they speak,) I thought fit to make the best shift I could to make the Tryal, of which I now proceed to give Your Lordship an Ac∣count.

The place I borrowed for this purpose was a flat Roof about 30 foot high from the ground, and with Railes along the edges

of it. The Tube we made use of should have been of Glass, if we could have procured one long and strong enough. But that being exceeding difficult, especially for me, who was not near a Glass-house, we were fain to cause a Tin-man to make several Pipes of above an inch bore, (for of a great length 'twas alleadg'd they could not be made slenderer,) and as long as he could, of Tin or Laton, as they call thin Plates of Iron Tinn'd over; and these being very carefully soder'd together made up one Pipe, of about one or two and thirty foot long, which being tied to a Pole we tried with Water whether it were stanch, and by the effluxi∣ons of that Liquor finding where the Leaks were, we caus'd them to be stopt with Soder, and then for greater security the whole Pipe, especially at the Commissures, was diligently cas'd over with our close black Cement, upon which Plaister of Paris was strewed to keep it from sticking to their hands or cloaths that should manage the Pipe. At the upper part of which was very carefully fastned with the like Cement a strong Pipe of Glass, of between 2 and 3 foot in length, that we might see what should happen at the top of the water. And to the upper part of this Pipe was (with Cement, and by the means of a short elbow of Tin) very closely fastned another Pipe of the same Metal, consi∣sting of two pieces, making a right Angle with one another, whereof the upper part was parallel to the Horizon, and the o∣ther, which was parallel to the Glass-pipe, reacht down to the Engine, which was plac'd on the flat Roof, and was to be with good Cement sollicitously fastned to the lower end of this descen∣ding part of the Pipe, whose Horizontal leg was supported by a piece of Wood, nail'd to the above mentioned Rails; as the Tube also was kept from overmuch shaking by a board, (fasten'd to the same Rails,) and having a deep Notch cut in it, for the Tube to be inserted into.

This Apparatus being made, and the whole Tube with its Pole erected along the Wall, and fastned with strings and other helps, and the descending Pipe being carefully cemented on

to the Engine, there was plac'd under the bottom of the long Tube a convenient vessel, whereinto so much Water was poured, as reach'd a great way above the orifice of the Pipe, and one was appointed to stand by to pour in more as need should require, that the vessel might be still kept competently full.

After all this the Pump was set on work, but when the water had been raised to a great height, and consequently had a great Pressure against the sides of the Tube, a small Leak or two was either discovered or made, which without moving the Tube we caus'd to be well stopt, by one that was sent up a Ladder to apply store of Cement where it was requisite.

Wherefore at length we were able after a pretty number of Exuctions, to raise the Water to the middle of the Glass-pipe a∣bove mentioned, but not without great store of bubbles, (made by the Air formerly conceal'd in the pores of the water, and now emerging,) which for a pretty while kept a kind of Foam upon the surface of it, (fresh ones continually succeeding those that broke.) And finding the Engine and Tube as stanch as could be well expected, I thought it a fit season to trie what was the utmost height to which Water could by Suction be elevated; and there∣fore though the Pump seem'd to have been plyed enough alrea∣dy, yet for further satisfaction, when the Water was within few inches of the top of the Glass, I caus'd 20 Exuctions more to be nimbly made, to be sure that the water should be raised as high as by our Pump it could be possibly. And having taken notice where the Surface rested, and caus'd a piece of Cement to be stuck near it, (for we could not then come to reach it exactly,) and de∣scending to the Ground where the stagnant water stood, we caus'd a string to be let down, with a weight hanging at the end of it, which we applied to a mark, that had been purposely made at that part of the (Metalline) Tube, which the superficies of the stagnant water had rested at, when the water was elevated to its full height: and the other end of the string being, by him that let it down, applied to that part of the Glass, as near as he could guess,

where the upper part of the Water reacht, the Weight was pull'd up; and the length of the string, and (consequently) the height of the Cylinder of Water was measur'd, which amounted to 33 foot, and about 6 inches. Which done, I return'd to my lodg∣ing, which was not far off, to look upon the Baroscope, to be in∣formed of the present weight of the Atmosphere, which I found to be but moderate, the Quick-silver standing at 29 inches, and be∣tween 2 and 3 eights of an inch. This being taken notice of, it was not difficult to compare the success of the Experiment with our Hypothesis. For if we suppose the most received proportion in bulk between Cylinders of Quick-silver and of Water of the same weight, namely that of 1 to 14, the height of the water ought to have been 34 foot and about two inches, which is about 8 inches greater than we found it. But then Your Lordship may be pleased to remember, that I formerly noted (before ever I made this Experiment) that I did not allow the proportion be∣twixt Mercury and Water (at least such water as I made my Tryals with) to be altogether so great, and though in ordinary Experiments we may with very litle inconvenience make use of that proportion to avoid fractions, yet in so tall a Cylinder of Water as ours was, the difference is too considerable to be neg∣lected. If therefore in stead of making an Inch of Quick-silver equivalent to 14 inches of Water, we abate but a quarter of an inch, which is but a 56 part of the height of the Water, this a∣batement being repeated 29 times and a quarter, will amount to 7 inches, and above a quarter, which added to the former height of the Water, namely 33 Foot and 6 inches, will make up 34 foot and above an inch; so that the difference between the height of the Mercury sustain'd by the weight of the Atmosphere in the Baroscope, and that of the Water rais'd and sustain'd by the Pres∣sure of the same Atmosphere in the long Tube did not appear to differ more than an Inch or two from the proportion they ought to have had, according to the difference of their specifick Gravi∣ties. And though in our Experiment the difference had been

greater, provided it exceeded not 8 or 10 Inches, it would not have been strange: partly, because of the difficulty of mea∣suring all things so exactly in such an Experiment, partly because as Waters are not all of the same weight, so a lit∣tle disparity of it in so long a Cylinder may be considerable, and partly (and perhaps chiefly) because the Air flying out of the bubbles, that rose out of so great a quantity of water, and break∣ing at the top of it, and so near that of the Tube, might by its Spring (though but very weak) assisting the weight of so much water, somewhat (though not much) hinder the utmost elevation of that Liquor. But our Experiment did not make it needful for me to insist on these considerations, and the inconsiderable difference that was betwixt the height of the water we found, and that which might have been wish'd, did rather countenance then at all difavour the thing to be made out by our Experiment, since by no Pumping we could raise the Water quite so high (though I confess it wanted but very little) as the weight of the At∣mosphere was able to keep up a Cylinder of Mercury proportio∣nable to it in height, and equivalent in weight: and yet I pre∣sume, Your Lordship will easily grant, that there was at least as much care used in this Experiment, to keep the things imploy'd about it tight, as has been wont to be used by Tradesmen in their Pumps, where tis not so easie either to prevent a little insinuation of the Air, or to discern it.

Tis not that I am sure, that even all our care would have kept the water for any long time at its full height; but, that the Air was sufficiently exhausted for our purpose, when we determin'd the height of the water, I was induc'd to conclude by these Cir∣cumstances.

1. As well the construction of the Engine, as the many (for∣merly related) Experiments, that have been successfully tryed with it, shew that tis not like it should be inferiour in closeness to the great Water-Pumps, made by ordinary Tradesmen: and par∣ticularly

the XI. Experiment foregoing, manifests, that by this Pump Quick-silver was rais'd to as great a height, as the Atmo∣sphere is able to support in the Torricellian Experiment.

2. The stanchness of the Pipe appear'd by the Diminution (as to number) of Bubbles, that appear'd at the top of the Water, and by their size too, for when there was a leak, (though but so very small, that the water could not get out at it in the Tube,) it might usually be taken notice of by the attentive ear of him that stood to watch upon the Ladder, erected by the side of the Tube; and the Air that got in, did easily discover it self to the Eye by large Bubbles, manifestly differing from those that came from the Aerial particles belonging to the water; and if the leak were not so very small, the Air that got in would suddenly lift up the water above it, and perhaps fill with it the descending Pipe.

3. Though there had been some imperceptible Leak, yet that would not have hindred the success of the Experiment for the main. For in leaks that have been but small, though manifest enough, we have often, by causing the Pump to be ply'd less nim∣bly then it now was, been able to prosecute our Tryals; because the Pump carried of still more Air than could get in at a leak that was no greater.

4. And that litle or no (intruding) Air was left in the upper part of our Tube, was evident by those marks, whereby it was ea∣sie for them that are well acquainted with the Pump, to estimate what Air is left in the vessel it should exhaust, and particularly to∣wards the end of our operation I observ'd, that when the Sucker was deprest, there came out of the Water that cover'd the Pump, so very few bubbles, that they might be imputed to the Air af∣forded by the Bubbles, springing from the water in the Tube; whereas if any adventious Air had got into that Cylinder of water, it would have appear'd in the water that cover'd the Pump.

5. Lastly, it were very strange, that if the water was but casu∣ally

hindred by some Leak from ascending any higher, it should be so easy to raise it to the very number of feet that our Hypothe∣sis requires, and yet we should be unable by obstinate Pumping to raise it one foot higher.

Note, 1. as soon as we had made our Experiment, and thereby found, that what was requisite to it was in order; I sent to give notice of it to D^r Wallis, and D^r Wren, as Persons whose curiosity makes them as well delighted with such Tryals, as their deep knowledg makes Them most competent Judges of them. But before They could be found, and come, it being grown somewhat late and windy, I that was not very well, and had tired my self with going up and down, could not stay with them so long as I intended, but leaving the rest of the Repeated Experiment to be shewn them by I. M. (who had been very industrious in fitting and erecting the Tube) they and their Learned friend (whom they brought with them) Doctor Millington, told me a while after, that they also had found the greatest height, to which they could raise the water, to be 33 foot and an half.

2. When the Water began first to appear in the Glass, the Bubbles would be, as I had foretold, exceeding numerous; so as to make a froath of near a foot high, if the water were newly brought, and had never been rais'd in the Tube before. But if the Pumping were long continued, the number and height (or at least one of the two) of the Aggregate of Bubbles, would (as there remain'd fewer and fewer Aerial particles in the water) be les∣ser and lesser; but their emerging did never that I remember wholly cease.

3. At the beginning also there would appear great vibrations of the water in the upper part of the Tube; the rising and the fal∣ling amounting sometimes to a foot, or near half a yard: but these grew lesser and lesser, as those of the Quicksilver in the Torricel∣lian Experiment use to do.

4. One may use an ordinary Pail to hold the stagnant water; but we rather imploy'd a vessel of Earth made (for another pur∣pose)

somewhat slender, and of a Cylindrical shape, because in a narrow vessel tis more easie to guess by the rising and falling of the Liquor, how the Pump is ply'd, and to perceive even smaller Leaks.

5. I must not forget to take notice, that though the newly nam'd Gentlemen came to me (when they had seen the Experi∣ment tryed) within less than an hour after the time I had look'd upon the Baroscope, and observ'd the Quick-silver to stand some∣what beneath 29 inches, and 3 eights; yet when presently upon their return I consulted the same instrument again, the Mercury appear'd to be sensibly risen, being somewhat (though but very litle) above 9 and 20 inches, and 3 eights, and 5 or 6 hours af∣ter (at bed-time) I found it to be yet more considerably risen. Which may keep Your Lordship from wondring at what I inti∣mated a little above, touching Monsieur Paschal's Experiment, as well as touching the disappointment of the Pump-makers en∣deavours. For tis not onely possible, that (as I have elsewhere noted) Water may be raised in the same Pump (though we sup∣pose it still equally stanch) higher at one time than at another: but 'twas contingent, that, in Monsieur Paschal's noble attempt to imitate the Torricellian Experiment with Water in stead of Quick-silver, the proportion betwixt the heights of those two Liquors in their respective Tubes answer'd so well to their speci∣fick Gravities. For, the varying weight of the Atmosphere be∣ing not then (that appears) known, or consequently taken into consideration; if Monsieur Paschal, having tryed the Torricellian Experiment, when the Air was for instance very heavy, had tryed his own Experiment, when the Atmosphere had been as light as I have often enough observ'd it to be, he might have found his Cylinder of Water to have been half a Yard or two foot shorter than the formerly measur'd height of the Quick-silver would have required.

I have now no more to adde about this 15^th Experiment, but that it may serve for a sufficient confirmation of what I note in a∣nother

Treatise, against those Hydraulical & Pneumatical Wri∣ters, who pretend to teach wayes of making Water pass by infle∣cted Pipes, and by the help of Suction, from one side of a Moun∣tain to the other, be the Mountain never so high. For, if the Water be to ascend as 'twere spontaneously above 35 or 36 foot, a Sucking Pump will not ordinarily, at least here in England, be able to raise it.

And now I speak of Mountains, it will not be altogether im∣pertinent to add, that if it had not been for unseasonable weather, I had thought fit to make the foregoing 11^th Experiment (of e∣levating Mercury by Suction) to be tryed at the top of an Hill, not far from the place I then was at. For by what has been al∣ready delivered, it appears, that we might have estimated the height, to which the Water may be there elevated by Suction, without repeating the Experiment with a thirty five foot Tube, (which we could not hope for conveniency to do,) by the utmost height to which our Engine could have rais'd Mercury: and it may be of some use to be able from Experiments to make some estimate (for it can scarce be an accurate one) how much it may be expected, that Pumps shall (caeteris paribus) loose of their power of elevating Water by Suction, by being imploy'd at the top of an Hill, in stead of being so at the bottom, or on a Plain. Re∣membring always what I lately intimated, that even in the same place Liquors will be brought to ascend by Suction to a greater or less height at one time than another, according to the varying Gravity of the Atmosphere.

Notes

• See plate the Figure the