Hydraulics*

o r Tides happen not on the Day of the Syzygy,^>ihr adrature =' ^ ut on 3^ or 4 th after ; the Sum orlitl t ^ nce of the Forces of the Luminaries not being

,. 34 -

« E «i>

at

IO9

a Maximum.

Fet S F E G be the Orbit of the Moon aboutsy. . lr ^ QN OP, which as it is not circular butV?ay 1Ca > Ae Centre of the Earth T will not be al-Moo 3t , an e qual Distance from the Moon ; but the8, a Will be sometimes nearest the Earth, as when atis Ca jj foretimes farthest off, as at E. The Point S4 p 0 „ ea the Perigaum, or Perigee ; and the Point E thePerf^^’ or Apogee. The Power of the Moon in herT * s to that in the Apogee nearly as TE 3 tothe jj’ an d consequently the greatest Tides will be onthe °f the Perigee, or rather a few Days after, for■Jr e ^s° ns above-mention’d.

I s Or j t ni s is very nearly agreeable to Experience,the^ the Year 17x3, February 26, the Elevation of, ate r at Brijlol was 22 Feet 5 Inches; and onthe / . t3, it was 18 Feet 2 Inches. The Moon, inEarth 1 * ^ al ' e » was * n f |er perigee, and distant from thetOQQ 953 Parts, of which the Mean-Distance containshe r A. In the latter Cafe she was in her Apogee, and^et. ance was 1032. Now 1032 3 : 953 s :: 22sthe a’, *7 Feet 8 Inches, which is but 6 Inches less thant( lUa) • ltu de observed. All other Circumstances were3 h/T ^oth Cafes.

the 55* Fke Manner, since the Earth moves aboutthe § ail » in an Orbit in some small Degree elliptical,that ; S 11 y^iH be at one Time nearest to the Earth (andt i le Perihelion) and at another Time farthestw . r om it (which is then call’d the Aphelion.)a rv tlle ^' ar tF * s * n Fer Perihelion , ( December)Water s ^fter, the Force of the Sun tcrmove the

Jkn e \ 5 Will be greater than when in her Aphelion (intl>n ber 5 o*' llus it was observed in the Year 1712, De~^June tlle Water ascended 19 Feet 2 Inches, and!he f *9 (of the preceding Year) it ascended but tok^°°n of t8 Feet 4 Inches: The Distance of thefound C ' ** e ' n S the fame in each Cafe, which willnearly to answer to the Ratio of the Cubes of

the

P’ate

XXVI.

rig.