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 ...

The I. Tryal.

We took a Syringe of Brass, (that Metal being closer and stron∣ger then Pewter, of which such instruments are usually made,) being in length (in the Barrel) about 6 inches, and in Diameter a∣bout 1 inch ⅜ and having, by putting a thin Bladder about the Sucker, and by pouring a litle Oyl into the cavity of the Cylin∣der (or Barrel,) brought the instrument to be stanch enough, and yet the Sucker to move to and fro without much difficulty, we thrust this to the bottom (or Basis) of the Barrel to exclude the Air, and having unscrew'd and laid aside the slender Pipe of the Syringe (which in this and some other Tryals was like to prove not onely needless, but inconvenient) we carefully stopt the Ori∣fice, to which the Pipe in these instruments is wont to be screw'd, and then drawing up the Sucker we let it go, to judg by the vio∣lence, with which it would be driven back again, whether the Sy∣ringe were light enough for our purpose, and finding it to be so, we fastned to the Barrel a ponderous piece of Iron to keep it down, and then fastning to the handle of the Rammer (or Axle-tree of the Sucker) one end of a String, whose other end was tied to the often mentioned turning-key: We convey'd this Syringe, and the weight belonging unto it, into a Receiver; and having pump'd out the Air, we then began to turn the Key, thereby to shorten the String that tied the handle of the Syringe to it; and, as we foretold, that the Pressure of the Air, lately included in the Receiver, being withdrawn, we should no more find the wonted

resistance in drawing up the Sucker from the bottom of the Cy∣linder, so we found upon Tryal that we could very easily pull it up without finding any sensible resistance.

However having thought fit to repeat the Experiment, (which we did with the like success,) lest it might might be objected, that this want of resistance might proceed, as partly from our im∣ploying the Turning-key to raise the Sucker, so principally from some unperceived Leak, at which the Air may be suppos'd to have got into the cavity of the Cylinder; I thought fit not onely to examine by Tryal, after the Receiver was remov'd from off the Pump, whether the Syringe were not stanch, (upon which I found that I could not, without some straining, draw up the Suck∣er even a litle way, and that it would be violently beaten back a∣gain,) but also in one of these Experiments to make this variation; That when, the Receiver being exhausted, we had drawn up the Sucker almost to the top of the Barrel by such a string as was pur∣posely chosen somewhat weak, we kept the parts of the Syring in that posture, till we had open'd a passage to the outward Air, up∣on whose ingress the Sucker was (as we intended it should be) so forceably deprest, that it broke the String by which it was tied to the Turning-key, and was violently driven back to the lower part of the Barrel, & that notwithstanding these two disadvantageous Circumstances; one, that the string was not so weak, but that one, whom I imploy'd to try it before it was fastned to the Syringe, made it sustain a lump of Iron that weighed between four and five pound; and the other, that yet this string was broken long before all the Air, that flowed in to fill the Receiver, had got in: so that the pressure of all the admitted Air would doubtless have broken a much stronger string, if we had imploy'd such a one to resist the depression of the Sucker, which will yet be more evident by a phaenomenon of our Syringe, that I shall presently have occasion to relate.