J. Ferguson inv. et del.
J. Mynde Sculp.
Turn the Handle until the Moon M comes to any given day of her age in the Circle of 291⁄2 equal parts, and the Moon’s Wire W will cut the time of her coming to the Meridian on that day, in the Hour Circle; the XII under the Sun being Mid-day, and the opposite XII Mid-night: then looking for the name of any given place on the round Plate (which makes 291⁄2 rotations whilst the Moon M makes only one revolution from the Sun to the Sun again) turn the Handle till that place comes to the word High Water under the Moon, and the Index which falls among the Afternoon Hours will shew the time of high water at that place in the Afternoon of the given day: then turn the Plate half round, till the same place comes to the opposite High Water Mark, and the Index will shew the time of High Water in the Forenoon at that place. And thus, as all the different places come successively under and opposite to the Moon, the Indexes shew the times of High Water at them in both parts of the day: and when the same places come to the Low Water Marks the Indexes shew the times of Low Water. For about two days before and after the times of New and Full Moon, the two small Plates come out a little way from below the High Water Marks on the elliptical Plate, to shew that the Tides rise still higher about these times: and about the Quarters, the other two Plates come out a little from under the Low Water Marks towards the Sun and on the opposite side, shewing that the Tides of Flood rise not then so high, nor do the Tides of Ebb fall so low, as at other times.
By pulling the Handle a little way outward, it is disengaged from the Wheel-work, and then the upper Plate may be turned round quickly by hand so, as the Moon may be brought to any given day of her age in about a quarter of a minute.
The inside work described.
Fig. VIII.
On AB, the Axis of the Handle H, is an endless Screw C which turns the Wheel FED of 24 teeth round in 24 revolutions of the Handle: this Wheel turns another ONG of 48 teeth, and on its Axis is the Pinion PQ of four leaves which turns the Wheel LKI of 59 teeth round in 291⁄2 turnings or rotations of the Wheel FED, or in 708 revolutions of the Handle, which is the number of Hours in a synodical revolution of the Moon. The round Plate with the names of Places upon it is fixed on the Axis of the Wheel FED; and the Elliptical or Tide-Plate with the Moon fixed to it is upon the Axis of the Wheel LKI; consequently, the former makes 291⁄2 revolutions in the time that the latter makes one. The whole Wheel FED with the endless Screw C, and dotted part of the Axis of the Handle AB, together with the dotted part of the Wheel ONG, lie hid below the large Wheel LKI.
Fig. 9th represents the under side of the Elliptical or Tide-Plate abcd, with the four small Plates ABCD, EFGH, IKLM, NOPQ upon it: each of which has two slits as TT, SS, RR, UU sliding on two Pins as nn, fixed in the elliptical Plate. In the four small Plates are fixed four Pins at W, X, Y, and Z; all of which work in an elliptic Groove oooo on the cover of the Box below the elliptical Plate; the longest Axis of this Groove being in a right line with the Sun and Full Moon. Consequently, when the Moon is in Conjunction or Opposition, the Pins W and X thrust out the Plates ABCD and IKLM a little beyond the ends of the elliptic Plate at d and b, to f and e; whilst the Pins Y and Z draw in the Plates EFGH and NOPQ quite under the elliptic Plate to g and h. But, when the Moon comes to her first or third Quarter, the elliptic Plate lies across the fixed elliptic Groove in which the Pins work; and therefore the end Plates ABCD and IKLM are drawn in below the great Plate, and the other two Plates EFGH and NOPQ are thrust out beyond it to a and c. When the Moon is in her Octants the Pins V, X, Y, Z are in the parts o, o, o, o of the elliptic Groove, which parts are at a mean between the greatest and least distances from the Center q, and then all the four small Plates disappear below the great one.
The Eclipsareon.
[Pl. XIII.]
442. The Eclipsareon. This Piece of Mechanism exhibits the Time, Quantity, Duration, and Progress of solar Eclipses, at all Parts of the Earth.