BOOK III.] OF NATURAL PHILOSOPHY. 449 the Royal Observatory at Paris, Oh. 9' 20 ' : but the mean motion >f the inoon and of its apogee are not yet obtained with sufficient accuracy. PROPOSITION XXXVI. PROBLEM XVII. To find the force of the sun to move the sea. The sun's force Ml, or PT to disturb the motions of the moon, was (by Prop. XXV.) in the moon's quadratures, to the force of gravity with us, as 1 to 638092.6; and the force TM — LM or 2PK in the moon's syzygies is double that quantity. But, descending to the surface of the earth, these forces are diminished in proportion of the distances from the centre of the earth, that is, in the proportion of 60