❝tivation of it. But it is a Matter of no fmall.. "Surprise to think how inconfiderable a Progress "the Knowledge of Nature had made in former "Ages, when compared with the vaft Improve"ments it has received from the numberless Disco« veries of later Times; infomuch, that fome of "the Branches of Natural Philofophy, which at

this Day is almost compleat in all its Parts, were "utterly unknown till the last Century. If we look <into the Reason of this, we fhall find it to be

chiefly owing to the wrong Measures that were "taken by Philofophers of former Ages in their "Pursuits after natural Knowledge; for they, difre"garding Experiments, the only fure Foundation "whereon to build a rational Philofophy, bufied "themselves in framing Hypotheses for the Soluti"on of natural Appearances; which, as they were "Creatures of the Brain, without any Foundation

in Nature, were, generally fpeaking, fo lame and defective, as in many Cafes not to answer "those very Phoenomena for whofe Sakes they had been contrived: Whereas the Philofophers of

later Times, laying afide thofe falfe Lights, as "being of no other Ufe than to misguide the Un"derstanding in its Searches into Nature, betook "themselves to Experiments and Obfervations; "and from thence collected the genuine Powers "and Laws of Nature; which, with a proper Ap"plication, and the Affiftance of mathematical "Learning, enabled them to account for most of "the Properties and Operations of Bodies; and to "folve many Difficulties in the natural Appearances "which were utterly inexplicable on the Foot of

Hypothefes. By this Means has natural Philofophy, within the Compass of one Century, been "brought out of the greatest Darkness and Obfcu"rity into the cleareft Light.".

As

As this is the Path in which our Author has trod, and endeavoured to conduct his Difciples, fo I think we can hardly follow a more skilful Leader. His Inftructions are not Matters of mere Curiofity, they all relate to the most noble and useful Theories and Arts, and they are delivered as concifely, and at the fame time with as great Perfpicuity as Matters of fuch a Nature are capable of. I doubt not but this Character will be allowed by all the Readers of the Work itself; but to convince mine in fome Meafure of the Equity of it, I muft here adjoin a few Paffages that may be collected from thofe Parts of the Book which do not abfolutely depend on the Plates or Diagrams for being intelligible.

In the firft, fecond, and third Lectures, our Author confiders thofe Principles, Forces, or Powers, wherewith all Matter, fo far as Experience reaches, feems to be endued; and whereby all the Particles and Portions thereof act upon one another for producing most of the Phoenomena of Nature.

Such is that Property, as he fays, whereby the minute Parts of Matter do, in fome Circumftances, tend towards one another, which is commonly call'd Attraction; the Caufe whereof is, in a great Meafure unknown, though the Thing itself is manifeft from Experiments: "For if two polifhed Plates "of Brafs be laid one upon another, having their " contiguous Sides fmeared with Oil, they will co"here in vacuo, and with fuch Firmness, that when

they are fufpended, the Force of Gravity in the lower Plate will not fuffice to separate and pull ❝ them asunder.

"That the Cohesion of thefe Plates is to be attributed to the mutual Attractions of their contiguous Parts cannot admit of a Doubt, fince the "Preffure of the outward Air on their external Sur

faces (to whofe Force this Effect might other"wife have been attributed) is in this Cafe taken off.

"The

6.6

66

The Ufe of the Oil is to fill up the minute "Cavities in the Surfaces, and, by fo doing, to prevent the Lodgment of Air between the "Plates; which, upon the Removal of the outward Air, would expand itself by reafon of its Elafticity and thereby force the Plates afunder.*» There are fome other Experiments whereby our Author evinces this Power of Attraction in Bodies. For Inftance, the Rife of Fluids between two poJifhed Plates of Glafs, when, being fet parallel, and at very fmall Diftances from one another, their lower Edges are dipped therein. "The Reafon "why the Fluid afcends between the Plates is, that

thofe Parts of the Surfaces of the Glaffes which lie next above the Surface of the Fluid, and are " contiguous thereto, attract the Water, and by that Means caufe it to afcend; and this Afcent "continues till the Weight of the elevated Water "becomes equal to the Force of the attracting Surfaces, and then the Motion ceafes, the Water tending as much downward by the Force of its "own Gravity, as it doth upwards by the Attrac"tion of the Glaffes."

The Height to which a Fluid afcends between thefe parallel Planes is inverfely as their Diftance. Thus, our Author tells us, "If the Planes be di

ftant from one another about the hundredth Part "of an Inch, the Fluid will rife between them to "the Height of about an Inch; and if the Distance

be greater or lefs in any Proportion, the Height "will be reciprocally proportional to the Distance very nearly." Of this he affigns the following Caufe:

66

*The Oil promotes the Cohefion of the Plates, not merely by excluding the elaftick Air, which would prevent it, but allo pofitively, by filling up the Vacuities with attracting Particles; by which Means the attractive Power of the contiguous Surfaces s vallly increased.

« The

"The abfolute attractive Force of the Glaffes, <<< whereby the Water is raifed, continues unvaried "whatever be the Distance of the Glaffes; for the

66

<ter;

Height and Length of the Glass Surfaces, whofe Attractions influence the Afcent of the Water, "are always the fame, and confequently the at"tractive Force must be fo too; and therefore will conftantly fupport the fame Weight of Wabut the Quantity, and confequently the "Weight of the elevated Water, will always be the fame, if its Height be reciprocally as its Bafe, "that is in this Cafe, as the Distance of the Plates; "for the Length of the Bafe being equal to the Length of the Plates, it continues unvaried; and therefore the Bafe will ever be as its Breadth, that is, as the Interval between the Plates."

1

Another Experiment, to the fame Purpose as the foregoing, defcribed by our Author, is with Glafs Plates, which, instead of being fet parallel to one another, are made to meet at one of their Ends, and kept at a little Distance at the other: "Their

lower Edges being then dipped in Water, Spirit "of Wine, or any other convenient Liquor; the * inward Sides of the Plates being first moiftened with a clean Cloth dipped in the Liquor; the Liquor will rife between the Plates, and the upper Surface of the elevated Liquor will form a "Curve, the Heights of whofe feveral Points above "the Surface of the ftagnating Liquor will be to "one another reciprocally as their perpendicular "Distances from the Concourfe of the Plates." That the Phænomenon must be thus our Author formally demonftrates: But the Neceffity of its being fo may be easily collected from the two foregoing Paragraphs.

66 As Water (to ufe our Author's own Words) " or any other proper Fluid, afcends between po

"lished

lifhed Plates of Glafs by the Force of their At"tractions, so does it likewife in flender Pipes of "Glass open at both Ends; for if fuch Tubes be "dipped at one End into Water, Spirit of Wine, "or any other convenient Fluid, the Liquor will "rife within the Pipes to a confiderable Height; "and this Experiment alfo fucceeds in the very "fame Manner in vacuo, as in the open Air, for "the Liquor constantly ascends to the fame Height "in both.

"That the Afcent of Liquor in these small "Tubes, as also between polished Plates of Glass, "is to be attributed to fome Power in the Glafs "ftrongly acting on the Liquor, and not to the Pref"fure either of the ftagnating Liquor or incum"bent Atmosphere, is evident from this Confidera"tion; that as much of the Liquor remains fuf

66

pended in the Pipes, and between the Plates, "when they are lifted out of the ftagnating Fluid, "either in vacuo or the open Air, as was elevated "above the Surface of the Fluid, while they were

immerfed therein; and therefore whatever Caufe concurred to the elevating of the Liquor, while "the Plates and the Pipes were therein immerfed, " and exposed to the Air; the fame contributes as "powerfully to keep it up, when the stagnating Liquor is removed, and the Preffure of the At"mosphere taken off, and confequently must be "fome Power inherent in the Glass.

66

"The Heights to which the Liquor rifes in flen"der Pipes are to one another reciprocally as the "Diameters. For the Power which raises the Li

quor in a flender Pipe, being the attractive Force "of that Part only of the internal concave Surface "which lies next above the Liquor, and conftitutes "a Ring of an indefinitely fmall Height, which Height is ever the fame whatever be the Dia

"meter