An Account of Sir Isaac Newton's Philosophical Discoveries; In Four Books

This historic book may have numerous typos, missing text or index. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. 1750. Not illustrated. Excerpt: ... C H A P. VI. Of the figure of the earth, and the precession of the equinoxes. i. TF the earth was fluid, and had no motion on \_ its axis, the equal gravitation of its parts towards each other would give it a figure exactly spherical, the columns from the surface to the centre mutually sustaining each other at equal heights from it. But, because of the diurnal rotation of the earth on its axis, the gravity of the parts at the equator is diminished by the centrifugal force arising from this rotation; the gravity of the parts on either side of the equator is diminished less, as the velocity of rotation is less, and the centrifugal force, arising from it acts less directly against the gravity of the parts; while the gravity at the poles is not at all affected by the rotation. The equilibrium that was fupposed to be amongst the parts will not, therefore, now subsist in a spherical figure, but will be destroyed by the inequality of their gravitation, till the water rise at the equator and sink at the poles, so as, by a greater height at the equator, to compenfate the greater gravity at the poles; and till, by asfuming an intermediate height in the intermediate places, the whole earth become of an oblate spheroidal form, whose diameter. at the equator will be the greatest, and the axis the least, of all the lines that can pass through the centre. . 2. If the gravity of a body at the equator was destroyed, the motion of rotation would there make it go off in a tangent to the earth; and by moving in the tangent it would rife, in a second of time, . J' * from from the spherical body of the earth, as much as one extremity of the arc which bodies describe there, in a second, falls below the tangent drawn at the other extremity: and this is found to be a space of about ...