division of labour, produced in a judicious allotment, by more than one, we should probably witness, in a popular astronomical lecture, the richest intellectual treat the stage can afford us.

After this, we may be expected to speak of the qualifications of our two principal lecturers. Did the style of either of these gentlemen demand from a journalist any thing but unqualified commendation, our task might be an ungracious one. We have, however, but to describe in few words the difference in the style of delivery of the rival lecturers, and the peculiarities of each as to the mechanism they adopt, and the embellishments they respectively bestow on their exhibitions.

Of Mr. Walker, we will say, that the original transparent Orrery of his venerable father's construction, possesses a charm, an air of times gone by, which, by powerful association, rivets the attention; it has suffered nothing by time, but has the advantage of much additional embellishment, an art in which its style of early days could not have been adopted. In that direction, however, there is still much room for further exertion. Mr. Dean Walker, the present lecturer on the Eidouranion, is the second Walker in succession since the invention of his father. Mr. William Walker, the elder son, who for twenty years together read the only astronomical lecture we had, was the first; and, shortly after his decease, about seven years since, this heir-loom descended to its present proprietor. Mr. Walker is distinguished from his father and his deceased brother, in his public lectures, by a more polished and easy delivery, a graceful familiarity, which secures the attention of the young and the unlearned, and an elegance of diction and general manner, which greatly heightens the effect of his discourse to every class. It is with no invidious or unworthy feeling, that we say of Mr. Walker and the Eidouranion, as compared with other exhibitions of similar character, that we feel his lecture and his apparatus to be indeed the original, and experience an involuntary satisfaction, that the present arrangements of neither differ in their material points from those determined by the inventor more than half a century ago.

Mr. Bartley is entitled to our respectable consideration on different grounds. His exhibition is a theatrical adventure, of great merit and curiosity; creditable alike to those who have undertaken, and those who embody it. Mr. Bartley delivers his lecture with great solemnity and proper feeling, has evidently a sound perception of the subject, and the importance of his task, and delivers himself of it like a sensible man, feelingly alive to the dignity of his subject.

Parents will duly appreciate Mr. Bartley's exertions, in conveying to the minds of their children the lofty and magnificent ideas that Astronomy supplies.-Beauty, Order, and Sublimity in the Heavens, appear to their expanding intellect, in all their delightful prospects; and the feelings, that will certainly influence their entrée into life, will be characterized by a marked reverence for that

Adults, as well as

Divinity which breathes within us,
And points out an after state to man."

children, will derive, from this exhibition, an increased perception of the power, dignity, and ubiquity, of that Being whom we ought to serve.

THE SELF-MOVING ORRERY,

AND

THE ASTRONOMICAL EXHIBITIONS OF MODERN TIMES, Which add to their Mechanical Arrangements the Illustrations of Music, and Scenic Decorations.

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THE Busby Orrery, unquestionably the most beautiful contrivance of modern times, for the popular exhibition of Astronomical Phenomena, ranks high, as well for its mechanical merit, as its singular beauty of action: it is perly termed a self-acting machine, and, to the eye of taste, is equally charming in its conception, its organization, and its effect. The self-acting Hydraulic Orrery seems, indeed, to lay open a new field for the display of philosophical mechanism.

Mr. Busby, its inventor, was, it seems, engaged, some time back, in a series of experiments, to determine the resistances opposed to floating bodies passing through fluids; and his method of performing these will, we presume, be interesting to our scientific readers, both as it led to the invention of the machine we are about to describe, and as it exhibits the rationale of its construction.

A circular reservoir of water was provided, having a small perpendicular shaft erected in the centre, and the vessel which formed the particular sub

ject of experiment was placed upon the water, near the circumference, but connected with the centre, by an arbor extending to the shaft, and supported by a float. The vessel was pierced in the bottom, and the shorter extremity of a siphon being soldered into the opening, the longer leg hung over the circumference of the reservoir. This leg, unlike that of the ordinary siphon, was closed at the bottom, but a small aperture being made, the water spouted through it, in a direction at right angles to the arbor, and the vessel immediately began to move with accelerated velocity in an opposite course: in a second or two it arrived at a maximum, and the future progress exhibited that delightful, equable, gliding motion, which seems to afford the only true. similitude to the silent grandeur of the celestial movements.

The principle upon which this experiment was made, is that of the wellknown philosophical machine called "Barker's Mill;" but the grand improvement consisted in combining that principle with a siphon, supported by a floating body; by which means, a perfectly uniform head of water (and, consequently, of action) was preserved, and the mechanical friction almost annihilated.

Having completed his temporary experiments, the author next endeavoured to apply this beautiful combination to some other purpose of general usefulness; and it immediately occurred to him, that an Orrery might be so constructed upon hydraulic principles, as, by their instrumentality, to afford a more perfect and accurate representation of the harmonious movement of the heavenly bodies, than had yet been effected.

Orreries are now too generally known to be otherwise than familiar to every well-informed person: these instruments, however, have hitherto been constructed by a complication of wheel-work, which, although extremely ingenious, are nevertheless almost unequal to the imitation of those equable, silent, and undeviating movements, which characterize the grandest works of the Creator. The Hydraulic Orrery, on the contrary, possesses all the advantages of the former machines, together with the distinguishing characteristic of self-action, and a perfect imitation of the motions, as well as the positions, of the planetary bodies. It will be recollected that, to constitute an orrery, it is not necessary that the machine should include all the planets; a machine, which represents the motions of the sun, the earth, and the moon, is still an orrery; and to these bodies, with Jupiter and his satellites, Mr. Busby first applied his hydraulic principles. It appears, however, he has recently arranged and organized a plan for a more extensive Hydraulic Orrery, in which the most remote planets and their satellites are included.

In the centre of his exhibition room was placed a circular reservoir, five feet diameter. The Sun, represented by a ball of nine inches diameter, sustained upon a slender shaft, about two feet above the surface of the water, and borne by a small circular floating vessel in the middle of the reservoir; this vessel carried a syphon, which discharged a minute lateral stream into a separate, floating rim, or concentric circular vessel, which surrounds it. The re-action of this discharge causes the vessel bearing the Sun to revolve upon an axis erected in the centre of a bar, extended diametrically across the inner circle of the rim, or surrounding vessel. The water thus received into the room flows along a tube beneath the surface of a reservoir, and enters a floating cylindrical chamber at the other extremity. In the centre of this chamber a tube is erected, through which a forked rod passes, and bears. the Earth, represented by a ball of three

inches diameter, at an appropriate elevation, and having its axis duly inclined to the ecliptic. A separate floating rim surrounds the cylindric chamber, bearing the shaft which carries the Moon, on one side, and a reacting syphon on the other, the discharge from which impels it round the shaft which bears the Earth. This floating rim also acts, by contact, upon a small wheel, attached to a slender rod, communicating by an universal joint with the axis of the Earth, and thus causes that body to revolve; while the action of a vertical wheel, with a radiating axis rolling round a horizontal circle fixed to the rod sustaining the Earth, gives motion to a small crank, which imparts an ascending and descending motion to the Moon, and produces the obliquity of its orbit; and a calculated disparity between the diameters of the vertical wheel, and the circle upon which it rolls, causes these ascending and descending motions to take place in a less period than one revolution of the Moon, and thus gives the due changes of the nodes.

The shaft which bears the Earth is continued beneath the surface of the water, and a flat plate, of six inches diameter, is connected with a plate of equal diameter at the circumference, by three parallel and oblique rods extending to it at the bottom of the centre of the reservoir, thus preserving the parallelism of the Earth's axis, on a principle analogous to that of a parallel ruler, at the same time the lateral motion of the central vessel, bearing the Sun, is prevented by a spur, which embraces the circumference of the plate beneath.

But, as the water which is discharged by the two siphons already described, would soon fill the receptacles, the operation of a third siphon is introduced, which carries away the superfluous water, and, by its lateral discharge on the outside the general reservoir, gives the annual motion of the Earth and Moon about the Sun.

We have thus attempted to describe the construction of this beautiful machine, but mere description does but imperfectly convey an idea of its effect in action. Our plate correctly represents its appearance on an enlarged scale, and (on a design of our own) under circumstances which, in actual construction, would render it of delightful interest; but its evolutions must be seen to be understood, its novelty and beauty of action felt and appreciated. In another part of the room, an ingenious apparatus represented the planet Jupiter and his satellites. In this the planet is centrally supported on a circular floating vessel, and the satellites are borne by concentric floating vessels at their due distances, respectively, from the primary. The primary receives its motion by the action of a stream of rarefied air, which proceeds from the flame of a small lamp, and, acting against an inclined shade, or sail, is thrown out in an horizontal direction. Thus the circular vessel bearing Jupiter, is made to revolve; the motion of this vessel imparts a gyratory motion to the whole body of water, by transmission from the several concentric vessels; and the vessels bearing the satellites are, consequently, made to revolve by the action of the water itself, with velocities regularly diminishing as their distances from the primary increase.

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The Hydraulic Orrery, its inventor has justly observed, may be erected on the most extensive scale, on a natural or artificial basin in the open air, or would form an interesting appendage to a conservatory or aquarium; but, as there exists no practical obstruction to the erection of these beauti.ul orreries on the great scale, we venture to recommend them as suitable ornaments for all public places in which a suitable piece of water occupies a commanding site. And we are decidedly of opinion, that an arrangement

of this self-acting machinery, in any such situation, would do more to promote a love of science and general astronomical information, than any thing that has been yet effected with that intention.

RYLAND'S LIVING ORRERY.

The singular beauty and attractive simplicity of the Busby Orrery, and the unlimited scale on which it may be practically employed, is approached (it is certainly not equalled) by a contrivance for a popular exhibition of the planetary system, by John Ryland, in his elementary treatise of Mechanics, in the year 1768; and a more extensive and more perfectly organized arrangement, by De Vaux, announced in his treatise on the Longitude.-Ryland's description is simple and concise; he designates his arrangement as a living orrery, made with sixteen school-boys." And, speaking of astronomy as a science capable of popular illustration, he says,

"It may be taught them in their play-hours with as much pleasure as they learn to play at marbles, or drive an hoop for an hour or two; and this may be done in the following manner:

"Take sixteen blank cards; write on one, the Sun; a seventeenth boy of a large size must be used for the Sun in the centre, with his diameter, which is seven hundred thousand miles. On another card write Mercury, with his period, eighty-eight days, distance from the Sun thirty-two millions, diameter two thousand six hundred miles, and hourly motion, which is one hundred thousand miles. So go on to Venus, our Earth, Mars, Jupiter, and Saturn. Then write on your other cards the names and periods of the ten moons in our system. Having thus furnished your cards, then provide the orbits for these sham planets; go into any plain field or place, where boys can play; draw a circle of two hundred feet diameter, which you may easily do with a cord and a broom-stick, ordering one boy to hold the cord in the centre, while you describe the circle with the stick at the other end of the string. When you have formed your circle, divide the semidiameter into one hundred parts; if you choose exactness, take five of these parts from the centre, and describe a circle for Mercury's orbit; take seven parts for the orbit of Venus; ten parts for our Earth's orbit; fifteen parts for the orbit of Mars; fifty-two parts, that is fifty-two fee, for the orbit of Jupiter. And let the outward circle of a hundred feet represent the orbit of Saturn, which is the boundary of the Newtonian system. After this draw your circles for our Moon round the Earth, for Jupiter's moons round him, and, last of all, for Saturn's five moons. There is no occasion to be scrupulously exact till the boys are well versed in these first easy notions; reduce them to accuracy by degrees. Whiston's Astronomical Principles of Religion, and Ferguson's Astronomy, will furnish ample materials for all your purposes. Now begin your play; fix your boys in their circles, each with his card in his hand, and then put your orrery in motion, giving each boy a direction to move from west to east; Mercury to move swiftest, and the others in proportion to their distances, and each boy repeating in his turn the contents of his card, concerning his distance, magnitude, period, and hourly motion. Half an hour spent in this play once a week will, in the compass of a year, fix such clear and sure ideas of the solar system, as they can never forget to the last hour of their life; and will probably rouse sparks of genius, which will kindle into a bright and beautiful flame in the manly part of life.