LET. VIII. OF THE NATURE OF THE TIDES. IZ5

them. When the actions of the fun and moonconspire together, as at the time of new andfull moon, the flux and reflux becomes moreconsiderable; and these are then called theSpring Tides. But when one tends to elevatethe waters, whilst the other depresses them, asat the moon’s first and third quarters, the effectwill be exactly the contrary; the flux and reflux,instead of being augmented, as before, will now bediminished; and these are called the Neap Tides.

But as this is a matter of some importance, itmay be worth while to enter into a more minuteexplanation of it. For this purpose, let S re-Plate iii.present the sun, Z H N R the earth, and F and S 7C the moon at her full and change. Then, be-cause the sun S, and the new moon C, are nearlyin the fame right line with the center of theearth O, their actions will conspire together, andraise the water about the zenith Z, or the pointimmediately under them, to a greater height,than if only one of these forces acted alone.

But it has been fliewn, that when the ocean iselevated at the zenith Z, it is also elevated atthe opposite point, or nadir N, at the fame time;and, therefore, in this situation of the fun andmoon, the tides will be augmented. And again,whilst the full moon F raises the waters at Nand Z, directly under and opposite to her, thefun S, acting in the fame right line, will alsoraise the waters at the fame points Z and N,

K 4 directly