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 XXXIX.

About a further attempt to prosecute the Inquiry propos'd in the foregoing Experiment.

COnsidering with my self, that by the help of some contrivan∣ces not difficult, a Syringe might be made to serve, as far as our present occasion required, in stead of a pair of Bellows; I thought it would not be improper to try a differing, and, in some regards, a better way to prosecute an attempt, which seem'd to me to deserve our Curiosity.

I caus'd then to be made,* 1.1 for the formerly mentioned Syringe, in stead of its streight Pipe, a crooked one; whose shorter Leg was parallel to the longer. And this Pipe was for greater close∣ness, after 'twas screw'd on carefully, fastned with Cement to the Barrel; and because the Brass-pipe could scarce be made small e∣nough, we caus'd a short and very slender Pipe of Glass to be put into the orifice of the shorter Leg, and diligently fasten'd to it with close Cement. Then we caus'd the Sucker (by the help of Oyl, Water, and moving it up and down) to be made to go as smoothly as might be, without lessening the stanchness of the Sy∣ringe. After this, there was fastned to the handle of the Ram∣mer a Weight, made in the form of a Ring, or Hoop, which by reason of its figure might be suspended from the newly mention'd handle of the Rammer, and hang loose on the outside of the Cy∣linder, and which both by its Figure and its Weight might evenly and swiftly enough depress the Sucker, when That being drawn up the Weight should be let go. This Syringe thus furnished, was fastned to a broad and heavy Pedestal, to keep it in its verti∣cal posture, and to hinder it from Tottering, notwithstanding the Weight that clogg'd it. And besides all these things, there

was taken a Feather, which was about two inches long, and of which there was left at the end a piece about the breadth of a mans Thumb-naile, (the rest on either side of the slender stalk (if I may so call it) being stript off) to cover the hole of the slender Glass pipe of the Syringe; for which purpose the other extreme of it was so fastned with Cement to the lower part of the Syring, (or to its Pedestal,) that the broad end of the Feather was plac'd (as the other Feather was in the foregoing Experiment) just over the litle orifice of the Glass, at such a convenient distance, that when the Sucker was a litle (though but very litle) drawn up and let go again, the Weight would depress it fast enough to blow up the broad part of the Feather, as high as was permitted by the resistance of the Stalk, (and that was a good way,) the Spring of which would presently restore the whole Feather to its former position.

All these things being done, and the handle of the Rammer being tied to the Turning-key of a capp'd Receiver, the Syringe and its Pedestal were inclosed in a capacious Receiver, (for none but such a one could contain them, and give scope for the Ram∣mers motions,) and the Pump being set on worke, we did, after some quantity of Air was drawn out, raise the Sucker a litle by the help of the Turning-key, and then turning the same Key the contrary way we suffer'd the Weight to depress the Sucker, that we might see at what rate the Feather would be blown up; and finding that it was impell'd forceably enough, we caus'd the pum∣ping to be so continued, that a pretty many pauses were made, during each of which we rais'd and depress'd the Sucker as before, and had the opportunity to observe, That as the Receiver was more and more exhausted of the Air, so the Feather was less and less briskly driven up, till at length, when the Receiver was well emptied, the usual elevations and depressions of the Sucker would not blow it up at all that I could perceive, though they were far more frequently repeated than ever before; nor was I content to look heedfully my self, but I made one whom I had

often imploy'd about Pneumatical Experiments to watch atten∣tively, whilst I drew up, and let down the Sucker, but he affirm'd that he could not discern the least beginning of Ascension in the Feather. And indeed to both of us it seem'd, that the litle and inconsiderable motion that was sometimes (not alwayes) to be discern'd in the Feather, proceeded not from any thing that issued out of the Pipe, but from some litle Shake, which twas difficult not to give the Syringe and Pedestal, by the raising and depres∣sing of the Sucker.

And that which made our Phaenomenon the more considerable, was, that the Weight that carried down the Sucker being still the same, and the motions of the Turning-key being easie to be made equal at several times, there seem'd no reason to suspect that Contingencies did much (if at all) favour the success; but there hapned a thing, which did manifestly enough disfavour it. For I remember, that before the Syringe was put into the Recei∣ver, when we were trying how the Weight would depress it, and it was thought that though the Weight were conveniently shap'd, yet it was a litle of the least; I would not alter it, but foretold, that when the Air in the Cavity of the Syringe (that now resi∣sted the quickness of its descent, because so much Air could not easily and nimbly get out at so small a Pipe) should be exhausted with the other Air of the Receiver, the elevated Sucker would fall down more easily, which he, that was imploy'd to manage the Syringe whilst I watch'd the Feather, affirm'd himself afterwards to observe very evidently. So that when the Receiver was ex∣hausted, if there had been in the cavity of the Syringe a matter as fit as Air to make a Wind of, the Blast ought to have been Grea∣ter, because the celerity that the Sucker was deprest with was so.

After we had long enough tried in vain to raise the Feather, I order'd some Air to be let into the Receiver; and though when the admitted Air was but very litle, the motions of the Sucker had scarce if at all any sensible operation upon the Feather, yet when the quantity of Air began to be somewhat considerable,

the Feather began to be a litle mov'd upwards, and so by letting in Air not all at once but more and more from time to time, and by moving the Sucker up and down in the intervals of those times of admission, we had the opportunity to observe, that as the Receiver had more Air in it, the Feather would be more briskly blown up.

But not content with a single Tryal of an Experiment of this consequence, we caused the Receiver to be again exhausted, and prosecuted the Tryal with the like success as before, onely this one Circumstance, that we added for confirmation, may be befit to be here taken notice of. Having, after the Receiver was exhau∣sted, drawn up and let fall the Sucker divers times ineffectually; though hitherto we had not usually rais'd it any higher at a time, than we could by one turn of the hand, both because we could not so conveniently raise it higher by the Hand alone, and because we thought it unnecessary, since that height suffic'd to make the Air briskly toss up the Feather; yet ex abundanti we novv took an instrument that was pretty long and fit so to take hold on the Turning-key, that we could easily raise the Sucker between two and three inches (by our Aestimate) at a time, and nimbly depress it again; and for all this, which would much have increas'd the Blast, if there had been a Matter fit for it in the Cavity of the Sy∣ringe, we could not sensibly blow up the Feather, till we had let a litle Air into the Receiver.

To be able to make an aestimate of the Quantity of Air pump'd out, or let in, when the Feather vvas strongly or faintly, or not at all rais'd by the fall of the Sucker; vve took off the Re∣ceiver, and convey'd a Gage into it, but though for a vvhile vve made some use of our Gage, yet a mischance befalling it before the Operation was quite ended, I shall forbear to adde any thing concerning that Tryal, and proceed to say something of another Attempt, wherein though I foresaw and met with such difficul∣ties, as kept me from doing altogether what I desired, yet the suc∣cess being almost as good as could be expected, I shall venture

to acquaint Your Lordship with the Tryal, which was this.

In stead of the hitherto imploy'd Pipe of Brass, there was well fastned (with Cement) to the Syringe a Pipe of Glass, whose fi∣gure differ'd from that of the other in this particular, that the shorter (or remoter) Leg of our new Pipe, after it had for a while been carried parallel to the other Leg, was bent off so, that above an inch and a half of it tended downwards, that the orifice of it might be immerst into Water contain'd in a small open Jarr. The design of which contrivance was, that when the Receiver should be well exhausted, we might (according to what I told Your Lordship vvas at first design'd) try vvhether by the raising and depressing of the Sucker any such Matter would be driven out at the nose of the Pipe, as would produce bubbles in the incumbent Water, which, Air (though highly rarefied, perhaps to some hun∣dreds of times beyond its wonted Dimensions,) is capable of do∣ing. And I choose to imploy rather Water than Quick-silver, because though by using the later I might hope to be less trou∣bled with bubbles, yet the ponderousness and opacity of it seem'd to outweigh that convenience.

I need not tell Your Lordship, that in other respects this Ex∣periment was made like the former, so that I shall mention onely its peculiarities, which were, That as the Air was pump'd out of the Receiver, that in the Glass pipe made its way through the Water in Bubbles, and a litle Air having once by a small Leak got in, and forc'd some of the Water out of the Jarr into the pipe, when the Receiver was again vvell emptied, both that Water and even the litle quantity of stagnant Water, that was contain'd in the immerst part of the Pipe, produc'd so many bubbles of se∣veral sizes, as quite disturb'd our Observations. Wherefore we let alone the Receiver, exhausted as it was, for 6 or 7 hours, to give the Water time to be freed from Air, and then causing what Air might have stolen in to be again pump'd out, till we had per∣ceiv'd by the Gage that the Receiver was well exhausted, we caus'd the Sucker (of the Syringe) to be rais'd and deprest diverse

times, and though even then a Bubble vvould now and then make our Observations troublesome, and less certain, yet it seem'd to us, that when we were not thus confounded, we sometimes ob∣served that the elevation and fall of the Sucker, though reiterated, did not drive out at the Pipe any thing that made any discernable bubbles in the incumbent Water; for though there would appear now and then some small bubbles on the surface of the Water, yet I could not perceive that the Matter that made them, issued out at the Pipe; and some of them manifestly proceeded from A∣erial Particles, till then lurking in the Water, as I concluded from the place and time of their rising. But this Non-eruption of bubles at the nose of the Pipe, vvas not that which gave me the most of satisfaction. For at length both I and another had the opportunity to observe the Water in the immerst part of the Pipe, which was very slender, to be about an inch higher than the rest of the stagnant Water, and to continue at that height or place in the Pipe, though the Sucker vvere divers times together rais'd and depress'd by Guess between 2 and three inches at a time. Which seem'd to argue, either that there was a vacuum in the ca∣vity of the Syringe, or else that if it were full of Aether, that bo∣dy vvas so subtle, that the impulse it received from the falling Sucker vvould not make it displeace a very litle Thread (per∣haps not exceeding a Grain in Weight) of Water that vvas in the slender Pipe, though it appear'd by the bubbles, that sometimes disclos'd themselves in the Water, after the Receiver had been exhausted, that far more Water vvould be displac'd and carried up by a small bubble consisting of such rarified Air, that accor∣ding to my Aestimate the Aerial particles of it did not, before the Pump vvas begun to be set on vvork, take up in the Water a five-hundredth part of the quantity of a Pins head.

But whilst we were considering what to do further in our Try∣al, a litle Air, that strain'd in at some small undiscoverable Leak, drove the Water into the emptied part of the Pipe, and put an end for that time to our Tryal, which had been too toylsome to invite us then to reiterate it.

I had indeed thoughts of prosecuting the Enquiry, by dropping from the top of the exhausted Receiver light Bodies convenient∣ly shap'd, to be turn'd round, or otherwise put out of their sim∣plest motion of Descent, if they met with any resistance in their fall; and by making such Bodies move Horizontally and other∣wise in the Receiver, as vvould probably discover whither they were assisted by the medium: and other contrivances and wayes I had in my thoughts, whereby to prosecute our Enquiry, but vvanting time for other Experiments, I could not spare so much as was necessary to exhaust large Receivers so diligently, as such nice Trials would exact; and therefore I resolv'd to desist, till I had more leisure than I then had, (or have since been Master of.)

In the interim, thus much we seem to have already discovered by our past Tryals, that if when our Vessels are very diligently freed from Air, they are full of Aether, that Aether is such a bo∣dy, as will not be made sensibly to move a light Feather by such an impulse as would make the Air manifestly move it, not onely whilst tis no thinner than common Air, but when tis very highly rarified, (which, if I mistake not, it was in our Experiment so much, as to be brought to take up above an hundred times more room than before.)

And one thing more we gain'd by the Tryal made with water, namely a clear confirmation of what I deliver'd in the 34^th Ex∣periment, about the cause of the Suction that is made by Syrin∣ges; for Your Lordship may remember, that at the close of the Experiment we have all this while been reciting, I observ'd, that when the external Air was so very well withdrawn, the pulling up of the Sucker would not make the stagnant Water, that the Pipe of the Syringe was immerst in, to ascend one inch, or so much as the tenth part of it.

Notes

• * 1.1

  See plate the Figure the