36 meter of the Ring, because the Distance to which "the attractive Force of Glafs reaches is unvaried;

and the attractive Force of fuch an annular Surface "being as the Number of attracting Parts whereof "it is compofed, that is, as the Surface, which be"caufe its Height is given is as the Periphery, "that is, as the Diameter, the attractive Force of "the Pipe must be as the Diameter.".

It is, our Author fays, by Virtue of this attractive Force, wherewith fmall Pipes are endued, that Plants receive Nourishment from the Earth; the flender Tubes, whereof their Roots are compofed, fucking in various Juices, according to their different Natures and Conftitutions.

In this first Lecture there are three Experiments, befides those I have here recited: One is to prove that a Fluid rifes in the above mentioned and all fimilar Cafes, by the Action of thofe Particles alone which are contiguous to and lie next above the Surface of the elevated Matter; thofe Particles which are at any the leaft fenfible Distance above it being too far removed to influence it by their Attractions. The two laft are for determining the Force of Attraction of two Glafs Planes meeting in an Angle, at all Distances from the angular Point; or of conical Tubes, at all Distances from their Vertices. What our Author has offered upon thefe Heads is very curious. Towards the Clofe of this Difcourfe, he fays,

"The firm Union, and ftrong Cohesion of the "Particles of folid Bodies, feem to arife from "this Force wherewith they mutually attract each "other; which as it appears to be exceeding

Atrong in the immediate Contact of the Particles, "fo it is found, by Experience, to reach but a very little Way beyond the fame, with any fenfible "Effect. At very fmall Distances indeed it is fufficient to raife up Liquors, as alfo to produce

"the

"the many odd and furprifing Appearances which are to be met with in chymical Operations, and which without the Affiftance of this, as well as "fome other Principles, are utterly inexplicable." He afterwards points out fome of thofe many grofs Mistakes and Abfurdities in their Reafonings, which Chymifts have fallen into for Want of a due Knowledge of thefe Powers.

Having in his first Lecture proved from Experiments, that there is a Power in Nature, whereby the Parts of Matter, which are brought fo near as to touch, do in fome Circumftances mutually attract each other; our Author proceeds in the fecond to treat of fuch Kinds of Attraction as extend themfelves to confiderable Distances beyond the Point of Contact, and on that Account, as he fays, affect the Mind more ftrongly, fo as to convince it more fully of the reality of fuch a Principle. Of this kind is, Firft, that Attraction which obtains between Glafs and Glafs. Secondly, That of Electricity. Thirdly, The Attraction of Magnetifm. And lastly, That of Gravity. On all these he infifts in their Order. I fhall, as a further Specimen of this Work, tranfcribe here two Experiments that occur in this Lecture, one is to fhew the Law of magnetical Attraction; by the other we discover the Measure of the Velocity and Force of falling Bodies.

The first Experiment, or the Magnetical one, is this: "Let a Loadftone be fufpended at one "End of a Ballance, and counterpoifed by Weights " at the other; let a flat Piece of Iron be placed

beneath it at the Distance of four tenth Parts of ❝an Inch, the Stone will immediately defcend, " and adhere to the Iron: Let the Stone again "be removed to the fame Diftance, and a Weight

of four Grains, and four tenth Parts of a Grain, "be thrown into the Scale at the other End of the "Ballance;

Ballance; this Weight will be an exact Counter"ballance to the attractive Force, and prevent the "Descent of the Stone; but if any Part of the "Weight be taken out, the Attraction will pre

vail, and carry the Stone down. If the Stone be placed at half the former Distance, that is to fay, at the Distance of two tenth Parts of an "Inch above the Iron, the Weight neceffary to shinder its Defcent will be about feventeen Grains "and an half, that is to fay, at the two tenth Parts of an Inch above the Iron, the Weight neceflary to hinder its Defcent will be about feventeen Grains and an half, that is, four times as much "as before. Confequently the attractive Force of "the Stone, at the fingle Distance from the Iron, is to the fame at the double Distance as four to one, that is, reciprocally as the Squares of the "Distances."

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The other Experiment I was to recite will prove, that the Velocities, and confequently the Forces, of falling Bodies are as the Times of their Defcent, or as the Spaces defcribed. "For if a Weight of "eleven hundred Grains be let fall from the Height "of three Inches, fo as to ftrike one End of a "Ballance, its Force will be just sufficient to raise "a Pound Weight, at the other End of the Ballance, "to the Height of about the eighth or tenth Part "of an Inch; whereas, if the fame Body be required to raise a Weight of two Pounds to the "fame Height, it must be let fall from the Height "of twelve Inches; and if the Weight to be railed be three Pounds, then muft the moving Body *fall from the Height of twenty-feven Inches.

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"The Forces wherewith the defcending Body *ftrikes the End of the Ballance, are measured by "the Weights that are raised; which in this Cafe

are as one, two, and three; but the Forces where with one and the fame Body ftrikes, are as the "Velocities

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"Velocities of the Body: Wherefore, in the Cafe "before us, the Velocities acquired by the falling

Body, are as one, two, and three but the "Heights from which it defcends, in order to acquire thofe Velocities, are as one, four, and “nine; that is, as the Squares of the Velocities.

"If this Experiment be repeated with a Body "double in Weight to the former, viz. with one "of two thousand two hundred Grains; the Weights "raised by the Strokes will be two, four, and fix "Pounds, that is, double the former."

From what our Author has faid in this Lecture, on this Subject of Gravity, he deduces divers Conclufions: I will just name them. First, From the laft Experiment appears the Truth of that Rule, which collect the Quantity of Motion in any Body, by multiplying the Velocity of the Body into its Quantity of Matter. Secondly, From what he has proved concerning the Spaces defcribed by falling Bodies, it follows, that if the Time of a Body's Fall be divided into a Number of equal Parts, the Spaces through which it falls in each of those Parts of Time taken feparately, and in their Order, beginning from the firft, are as the odd Numbers taken likewise in their Order, beginning from Unity. Thirdly, From what has been faid, it alfo follows, that the Velocity acquired by a falling Body at the End of the Fall, is fuch as with an equable Motion would in the fame time, in which the Body fell, carry it thro' a Space double that of the Fall.

When he has established these Inferences, the Doctor proceeds to the Demonftration of fome other Phoenomena of Gravitation. For Inftance, he makes it appear, that as the Motion of Bodies falling from a State of Reft, is uniformly accelerated; fo on the contrary, the Motion of Bodies thrown upward, is uniformly retarded. Likewife, that the Force of Gravity at the Surface of the

Earth

Earth is fuch as, fetting afide the Refiftance of the Air, makes a Body falling from a State of Reft, to defcend thro' a Space of fixteen Feet and an Inch in a Second of Time. But this, as he afterwards tells us, is meant of fuch Places only as are in or near the Latitude of forty-nine Degrees; in Places more diftant from the Line, the Defcent being quicker, and more flow in those less distant: The chief Caufe of which Difference, as he fays, is the Rotation of the Earth about its Axis, whereby all Bodies on or near the Surface of it, are endued with a centrifugal Force, which acts in Oppofition to that of Gravity, and of course must leffen the fame; and the Diminution of Gravity, arifing from this Cause, must be greatest under the Equator, and grow lefs and lefs in the Approach to the Poles. The Reafons affigned for this are, Firft, "Because the centrifugal Force is greatest "at the Equator, and from thence towards the "Poles is continually diminished, fo as at laft to "vanish in the polar Point. For all Parts of the "Earth's Surface, with the Bodies thereto adjacent, "revolve in the fame time, either in the Equator "or in the Circles parallel thereto; but the Equa"tor is the largest of all thofe Circles, and the "others grow lefs and lefs, as they are more and "more diftant from it: Now the centrifugal "Forces of Bodies revolving in the fame time in "different Circles, being to one another as the "Radii of the Circles, (as is fhewn in another "Part of this Book) it follows, that the centrifugal Force muft be greatest at the Equator, and "thence be continually diminished towards the "Poles."-It must be fo, Secondly, "Becaufe un"der the Line the centrifugal Force acts in direct Oppofition to the Force of Gravity, whereas in "other Places it acts in an oblique Direction to it, "and of confequence must act lefs powerfully against

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