Pendulum

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"I shall explain a System of the World differing in many particulars from any yet known, answering in all things to the common Rules of Mechanical Motions: This depends upon three Suppositions. First, That all Cœlestial Bodies whatsoever, have an attraction or gravitating power towards their own Centers, whereby they attract not only their own parts, and keep them from flying from them, as we may observe the Earth to do, but that they do also attract all the other Cœlestial bodies that are within the sphere of their activity; and consequently that not only the Sun and Moon have an influence upon the body and motion the Earth, and the Earth upon them, but that Mercury also Venus, Mars, Saturn and Jupiter by their attractive powers, have a considerable influence upon its motion in the same manner the corresponding attractive power of the Earth hath a considerable influence upon every one of their motions also. The second supposition is this, That all bodies whatsoever that are put into a direct and simple motion, will continue to move forward in a straight line, till they are by some other effectual powers deflected and bent into a Motion, describing a Circle, Ellipse, or some other more compounded Curve Line. The third supposition is, That these attractive powers are so much the more powerful in operating, by how much the nearer the body wrought upon is to their own Centers. Now what these several degrees are I have not yet experimentally verified; but it is a notion, which if fully prosecuted as it ought to be, will mightily assist the Astronomer to reduce all the Cœlestial Motions to a certain rule, which I doubt will never be done true without it. He that understands the nature of the Circular Pendulum and Circular Motion, will easily understand the whole ground of this Principle, and will know where to find direction in Nature for the true stating thereof. This I only hint at present to such as have ability and opportunity of prosecuting this Inquiry, and are not wanting of Industry for observing and calculating, wishing heartily such may be found, having myself many other things in hand which I would first complete and therefore cannot so well attend it. But this I durst promise the Undertaker, that he will find all the Great Motions of the World to be influenced by this Principle, and that the true understanding thereof will be the true perfection of Astronomy."

- Pendulum

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"The length of the pendulum and that of the meridian are the two principal means offered by Nature for fixing the unity of linear measurements. Both being independent of moral revolutions, they can undergo no detectable alteration short of enormous changes in the physical constitution of the earth. The first method is easily applicable, but has the disadvantage of making the measurement of distance depend on two elements that are heterogeneous to it, gravity and time, the division of [the latter of] which, moreover, is arbitrary. It was decided, therefore, to adopt the second method, which appears to have been employed in early antiquity, so natural is it for man to relate the units of distance by which travels to the dimensions of the globe that he inhabits. In moving about this globe, he may thus know by the simple denomination of the distance the proportion it bears to the entire circumference of the earth. This has the further advantage of making nautical and celestial measurements correspond. The navigator often needs to determine, one from the other, the distance he has traversed and [the length of] the celestial arc lying between the zenith at this point of departure and that at his destination.It is important, therefore, that one of these magnitudes should be the expression of the other, with no difference except in the units. But to that end, the fundamental linear unit must be an aliquot part of the terrestrial meridian, which corresponds to one of the divisions of the curcumferance.Thus the choice of the meter came down to that of unity of angles."

- Pendulum

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