all the different and important Qualities of the Air) a very useful Contrivance. Having detained you, I think, long enough on this Sort of Inftrument, I fhall be glad of an Opportunity, when you are next at Leifure, to have your Inftructions concerning the Nature and Ufe of that very celebrated Machine, the AIR-PUMP, which I have heard fo much talk of, but have never yet seen any Experiment made with it.

Cleon. Our next Conversation, my Euphrofyne, will be on that Subject; and nothing which the Field of Philofophy affords can more highly gratify your Curiofity, or improve your Understanding, than Experiments made therewith. As we have now furveyed the Nature and principal Properties of the vaft furrounding Atmosphere, and alfo of many different Species of Meteors generated therein, I think, it will be proper for you to conclude, this Speculation at prefent, by reading the poetical Defcription of this Subject, by the Author of the Poem, called, Univerfal Beauty, which I fhall leave with you for that Purpose.

While Ocean thus the latent Store bequeaths,
Above, its humid Exhalation breaths;

Its Bofom pants beneath the vig'rous Heat,
And eager Beams th' expanding Surface beat ;
Infinuating, form the lucid Cell,

To Bladders the circumfluous Moisture fwell;
Th' inflated Vapours fpurn the nether Tide,
And mounted on the weigtier Ether ride;
As tho' in Scorn of gravitating Pow'r,
Sublime, the cloudy Congregations tour;
O'er torrid Climes, collect their fable Train,
And form Umbrellas for the panting Swain;
Or figur'd wanton in romantic Mould,
Careering Knights, and airy Ramparts hold;
(Imblaz'ning Beams the fitting Champions gild,
And various, paint the vifionary Field ;)
Sudden the loofe, inchanted Squadrons fly,
And fweep Delufion from the wond'ring Eye;
Thence, on the floating Atmosphere they fail,
And fteer precarious with the varying Gale;
Or hov'ring, with fufpended Wing delay,
And in Difdain the kindred Flood survey.

When lo! th' afflicting Æther checks their Pride,
Compreffing chill, the vain dilated Tide;
Their fhiv'ring Effence to its Center shrinks,
And a cold Nuptial their Coherence links,
With artful Touch, the curious Meteor forms;
Parent, prolific of falubrious Storms,
(When from on high the rapid Tempeft's hurl'd,
Enliv'ning as a Sneeze to Man's inferior World.)
The frigid Chemift culls the min'ral Store,
The glolly Sphærules of metallic Ore;
Sublimes with Nitre and fulphureous Foam,
And hoards Contagion in Heav'n's ample Dome;
Where Nature's Magazine fermenting lies,
Till the bright Ray athwart the Welkin flies,
High Rage the fmall Incendiary infpires,
Whofe kindling Touch the dread Artillery fires;
Quick, with Effufion wide, the Lightnings glare;
Difploding Bolts, the cloudy Entrails tear;
The cleanfing Flames sweep thro' th' etherial Room,
And fwift, the gross infectious Steam confume,
Our vital Element the Blaze refines,

While Man, ingrateful, at his Health repines.
With various Skill, the chilling Artist works,
And Operator chief, in ev'ry Meteor lurks;
Oft, where the Zenith's lofty Realms extend,
E'er Mifts, conglobing, by their Weight defcend,
With fudden Nitre captivates the Cloud,
And o'er the Vapour throws a whitening Shroud:
Soft, from the Concave, hov'ring Fleeces fall,
Whofe flaky Texture cloaths our Silver Ball.
Or when the Show'r forfakes the fable Skies;
Hap'ly, the Cold in fecret Ambush lies,
Couching, awaits in fome inferior Space,
And chills the Tempest with a quick embrace;
The chryftal Pellets at the Touch congeal,
And from the Ground rebounds the murm'ring Hail.
Or conftant, where this Artificer dwells,
And algid, from his Heights the Mift repels;
Th' ALMIGHTY ALCHYMIST his Limbeck rears;
His Lordly Taurus, or his Alpine Peers;
Sufpending Fogs around the Summit fpread,
And gloomy Columns crown each haughty Head,

Obftructed,

Obftructed, drench the conftipating Hell,
And foaking, thro' the porous Grit distil;
Collecting from a thousand thousand Cells
The fubterraneous Flood impatient fwells;
Whence iffuing Torrents burft the Mountain's Side,
And hence impetuous pour their headlong Tide.*

DIALOGUE XI.

Of the INVENTION and CONSTRUCTION of the

AIR-PUMP.

Euphrofyne.

HE prefent Hour, I fee, is deftined for my InT formation in a Part of Knowledge that I have as yet few or no Ideas of.- -This Machine, I prefume, is what you call the Air-Pump; it appears to be of a curious Form and Make; and I fhall be highly pleas'd with a fhort Account of the original, or firft Invention of it. Can Can you tell any thing of that Matter, Cleonicus? Clean. The Inventor of this famous Machine was Otto Guericke, a Conful of Magdeburg, who, fome time before the Year 1654, first contrived and brought it into Ufe; for it was then, that this ingenious Gentleman, being employed in a public Negotiation at Ratisbon, had an Occafion offered him of fhewing his Inftrument to the Emperor, and fome other Princes there prefent; among whom, the Elector, and Archbishop of Mentz were particularly delighted with the Contrivance of the Inftrument, and the curious Experiments exhibited by it; infomuch that he became very defirous of having fuch another Machine made for his own Ufe: But this could not eafily be effected, by Reafon of the fhort Stay they had to make at Ratisbon, and for want of skilful Workmen. However, he prevailed with the Inventor to part with his own Apparatus; and at his Return, carried it home with him to Wurtzburg. Here it was, that the learned and diligent Jefuit, Father Schottus, being then Profeffor of the Mathematics in that Univerfity, had the first Sight of it, together with fome other VOL. I. curious

A a

curious and learned Perfons. The Archbishop was plea fed to give them an Account of the Engine; and a Relation of the Experiments he had feen the Inventor perform at Ratisbon. These they tried over feveral Times in his Prefence; and it was not long before they themselves alfo made feveral other new ones of the like Nature.

Euphrof. I do not wonder at their being highly delighted with fuch a curious Invention, and which, I fuppofe, foon made a great Noife in the World at that Time, and foon reached the Ears of most of the Virtuof in Europe.

Cleon. Indeed it did; principally by Means of the large Correfpondence which Schottus held with learned Men in most Parts of Europe; but more especially by a Book, which he published in the Year 1657, in which, and in an Appendix added thereto, he gave a diftinct and full Account of this Machine, and the Magdeburgic Experiments, as he calls them. After this, in the Year 1664, he published another Book, giving a farther Account of the Experiments that had been made fince the printing his former; and laft of all, in the Year 1672, the famous Inventor himself, Otto Guericke, was pleafed to give a moft perfect Narrative of his own Trials, in a Book, which he calls, New Magdeburgic Experiments in Vacuo. Thefe Books all explain the original Conftruction of this Inftrument, which, it muft be confefled, was very aukward and inperfect, in Comparison of the Forms in which they are now made; for in order to try Experiments with them, they were obliged to place their Glaffes, and other Veffels (from which they would exhauft the Air) under Water, in order to prevent the Air from getting in again.

Euphrof. No Wonder, if there has been a gradual and very confiderable Improvement in an Engine of fuch an extraordinary Nature, and I imagine, it was not long before fome of our British Geniuffes took it in Hand; for I have often heard it obferved, that the English never fail to improve upon the Hints they receive of any foreign Invention; and, indeed, I have heard fo much Talk of Boyle's Air-Pump, that I really took it for granted, he was the Inventor of it. I fuppofe, therefore, it was

he,

he, among our Countrymen, who first made any Progress in its Improvement.

Cleon. So far you are right, Sifter; and Multitudes think as you do, that Mr. Boyle was the Author of this Invention, from its having been fo generally called the Machina Boyliana; and the void Space produced by it, the Vacuum Boylianum: But thefe Appellations were rather the Confequence of his great Improvements in the Fabric of the Machine, the new Method of trying Experiments with it, and the numberless useful Purposes to which he applied them, the Glory of which has, in a Manner, totally obfcured all that had been heard of before in the Magdeburgic Experiments. Mr. Boyle himself gives a true Account of the Invention of this Machine, as I have now mentioned, in a Letter, which he wrote to his Nephew, the Lord Dungarvon, at Paris. Two Years after Schottus's Book was firft published, he does, indeed, fay, that he had fome Thoughts on the fame Subject before he had heard of those Gentlemens Performances Abroad; but that they had really anticipated him in the Invention of the Machine: But he obferves to his Lordship the great Imperfection the Invention then laboured under, and imployed two Gentlemen, Mr. Gratorix and Mr. Hooke, afterwards Dr. Hooke, to contrive fome Air-Pump, which need not, like that other, be kept under Water, and be more eafily and generally applied to Ufe, which after fome unfuccefsful Trials was at Length effected.

Euphrof. Are the Air-Pumps now in Ufe of this original Form of Mr. Boyle's.

Cleon. No; far enough from it: His own Alterations were not a few. Dr. Hooke's Pump ferved him not long; another Form, invented by Mr. Pappin, pleased Mr. Boyle ftill better, and fucceffive Changes and Improvements were made; till at laft, it arrived to the Perfection which it received from the Hands of that excellent Operator, the late Mr. Hawkfby, which is ftill one of the Forms in ufe; and is this large Engine, which you fee in this upright Frame.

Euphrof. An elegant and noble looking Machine, indeed. Pray, what may be the Expence of it?