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Of the ORRER Y.
Cleonicus. V ES, my Euphrosyne; this is the fam’d Machine, of
1 which I promised you the Sight and Use, when we last conversed on these Subjects,
Euphrof. A fhowy Piece of Art it seems to be, indeed! Pray, who was the first Inventor of it?
Cleon. This Machine was invented by Degrees, and made in its utmost Perfection, first by Mr. Rowley, for King George the First ; after which the Earl of Őrrery bespoke another; and from him, it is supposed by some, that it had its Name : But some will have it derived from a Greek Word of the fame Sound, which signifies to fee; because in this Machine we see all the Motions of the heavenly Bodies performed in the same Manner as they are in Nature itself.
Euphrof. Are there not different Sorts of Instruments of this Kind made; because, I think, I have seen the Print of an Orrery, of a different Make from this?
Cleon. Yes; since the first Invention they have been variously made, and very much improved by several Artists; but the Orrery constructed by the late ingenious Mr. Dean exceeds in Point of Neatness and Elegance all that has been yet made, if you except the Motions of the Satellites of Jupiter and Saturn; but there feems a great Deal wanting yet, to render an Orrery more simple in its Structure, and of an easier Purchafe than those which have been hitherto made ; for the first were sold for a thousand Guineas ; none of the largest Sort for less than three hundred.
Euphrof. Had the ancient Astronomers no Contrivance of this Kind, to represent the Motions of the heavenly Bodies ?
Cleon. Yes, it appears they had something analogous to it, made by that famous Mathematician, Archimedes, on whom the Latin Poet Claudian wrote a merry Epigram, in the English Translation of which you will see Rowe
ley's Name, instead of Archimedes, as given us by Dr. Harris in his astronomical Dialogue, Page 182.
IVhen lately Jove the Orrery survey'd,
Transplant him hither, and make him a Star. Euphrof. This is an ingenious Piece of Wit, indeed ; but the Instrument highly deserves it, to all Appearance ; it being in the external Frame, and (I doubt not) in the internal Structure, an admirably beautiful and exquisite Piece of Workmanship. .
Cleon. All you observe is very right; and Pity it is, that the Coftliness and Magnificence of so curious and useful an Instrument should be a Bar to its common Use. I shall now proceed to give you a View of each particular Part, in a general Description of the Whole.
The Frame, which contains the Wheel-work, &c. and regulates the whole Machine, is made of fine Ebony, and
into Degrees vi.cording to fome of through
is near four Feet in Diameter ; the Outside thereof is adorned with 12 Pilasters, curiously wrought and gilt : Between these, the twelve Signs of the Zodiac are neatly painted, with gilded Frames. Above the Frame is a broad Ring, supported with twelve Pillars ; this Ring represents the Plane of the Ecliptic, upon which there are two Circles of Degrees, and between these the Names and Characters of the twelve Signs. Near the Outside is a Circle of Months and Days, exactly corresponding to the Sun's Place at Noon, each Day throughout the Year.
Above the Ecliptic stand some of the principal Circles of the Sphere, according to their respective Situations in the Heavens, viz. (No. 1o.) are the two Colures, divided into Degrees and half Degrees. No. 11. is one Half the Equinoctial Circle, making an Angle of 231 Degrees. The Tropic of Cancer and the Arctic Circle are each fixed parallel, and at their proper Distance from the Equinoctial. On the Northern Half of the Ecliptic, is a Brass Semicircle, moveable upon two Points fixed in an and - : This Semi-circle serves as a moveable Horizon, to be put to any Degree of Latitude upon the North Part of the Meridian. The whole Machine is also so contrived, as to be set to any Latitude, without affecting any of the Inside Motions : For this purpose, there are two strong Hinges (No. 13.) fixed to the Bottom-Frame, upon which the Instrument moves ; and a strong Brass Arch, having Holes at every Degree, through which a strong Pin is to be put, according to the Elevation. This Arch and the two Hinges support the whole Machine, when it is lifted up, according to any Latitude; and the Arch, at other Times, lies conveniently under the BottomFrame.
When the Machine is set to any Latitude, (which is easily done by two Men, each taking hold of two Handles, conveniently fixed for that Purpose) set the moveable Horizon to the same Degree upon the Meridian, and you may form an Idea of the respective Altitude, or Depression of the Planets, both Primary and Secondary. 'The Sun (No. 1.) stands in the Middle of the whole System upon a Wire, making an Angle with the Plane of the Ecliptic of about 82 Degrees, which is the Inclination of the Sun's Axis, to the Axis of the Ecliptic.
Next the Sun is a small Ball (No. 2.) representing Mercury: Next to Mercury is Venus, (No. 3.) represented by a large Ball, and both these stand upon Wires, so that the Balls themselves may be more visibly perceived by the Eye. The Earth is represented (No. 4.) by an Ivory Ball, having some of the principal Meridians and Parallels, and a little Sketch of a Map described upon it. The Wire, which supports the Earth, 'makes an Angle with the Plane of the Ecliptic of 66; Degrees, which is the Inclination of the Earth's Axis to that of the Ecliptic. Near the Bottom of the Earth's Axis is a Dial-plate, (No. 9.) having an Index pointing to the Hours of the Day as the Earth turns round its Axis.
Round the Earth is a Ring, supported by two small Pillars; which Ring represents the Orbit of the Moon, and the Divisions upon it answer to the Moon's Latitude ; The Motion of this Ring represents the Motion of the Moon's Orbit, according to that of the Nodes. Within this Ring is the Moon, (No. 5.) having a black Cap, or Case, which by its Motion represents the Phases of the Moon, according to her Age.-Without the Orbits of the Earth and Moon is Mars (No. 6.) The next in Order to Mars is Jupiter, and his four Moons (No. 7.) Each of these Moons is supported by a crooked Wire, fixed in a Socket, which turns about the Pillar that supports Jupiter : These Satellites inay be turned by the Hand to any Position ; and yet when the Machine is put into Motion, they will all move in their proper Tiines. The outermost of all is Saturn, and his five Moons, and Ring, (No. 8.) These Moons are supported and contrived after the faine Manner with those of Yupiter. The whole Machine is put into Motion by turning a small Winch, like the Key of a Clock, (No. 14.) and all the Inside Work is so truly wrought, that it requires but very small Force to put the whole in Motion.
Euphrof. How are these planetary Bodies to be put in Motion Could I fee, or be made sensible of it?
Cleon. Yes: Above the Handle there is a cylindrical Pin, which inay be drawn a little out, or pushed in at Pleasure: When it is pushed in, all the Planets, both Primary and Secondary, will move according to their refpective Periods, by turning the Handle : When it is
to their Earth and in the Roamp, havina
drawn out, the Motion of the Satellites of Jupiter and Saturn will be stopped, while all the rest move without Interruption. This is a very good Contrivance to preserve the Instrument from being clogged by the swift Motions of the Wheels belonging to the Satellites of Jupiter and Saturn, when the Motion of the rest of the Planets are only considered.
There is also a Brass Lamp, having two Convex Glasses, to be put in the Room of the Sun; and also a smaller Earth and Moon, made somewhat in Proportion to their Distance from each other, which may be put on at Pleasure. !
The Lamp turns round at the same Time with the Earth, and by Means of the Glasses casts a strong Light upon her; And when the smaller Earth and Moon are placed on, it will be easy to fhew when either of them will be eclipsed.
Euphrof. Well ! I think every Thing adinirably adapted to answer the Purpose of such a Machine ; and now I presume you are ready to put it in Motion, and gratify my Sight with a view of the Secondary Planets as well as the Primary, in the various Revolutions, which I have not yet yet feen in any Inftruinent.
Cleon, I shall do it this Instant: You see I put on the Handle, and push in the Pin just above it; and place a black Patch (or Bit of Wafer) upon the Middle of the Sun, right against the first Degree of Aries (r). You may also place Patches upon Venus, Mars, and Jupiter, right against some noted Point in the Ecliptic. If you lay a Thread from the Sun to the first Degree of Aries (n), you may set a Mark where it intersects the Orbit of each Planet; and that will be a Help to note the Times of their Revolutions
Euphrof. Why am I to place Patches upon Venus, Mars, and Jupiter, and not upon Mercury and Saturn?
Cleon. Because these Planets are known to have a Motion about their Axis by a constant Observation of the Motion of Spots, seen on their Surfaces, when observed through good Telescopes. These Spots, like those of the Sun, are found to be regular, and to describe such Lines on the Surfaces of the Planets as they really would do, were the Planets to be moved about their Axis, with
the bit of cachon, may fet"a the sun toim