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Discourse on the Theory of the Planetary System.

tendency to one another. Yet since their tendency decreases as the square of the distance continually to all distances whatever, it follows, that if any number of stars be placed at any given distance from each other in space, in time they will be brought together, except some other power is admitted, to keep them in equilibrio.

From the different appearances of the various clusters of stars seen by the naked eye, and by the telescope, from the appearance of the milky way, and the nebulous or cloud-like spots seen in many parts of the heavens, it is clearly demonstrable, that the stars are not situated at equal distances from each other; nor can they be of equal magnitude. Some stars seem to have a small motion among the rest; some which were visible, have disappeared; and, on the contrary, some have become visible, which in ancient times were not so. These varied magnitudes and distances may be necessary to preserve them in equilibrio.

The planets do not move in the same plane, but in planes differently inclined to the sun's equator; and they revolve about the centre of the sun, although the whirling force lies in the direction parallel to his equator; for it must be observed, that the flowing force is at every instant tending to carry the planet toward the centre of the sun, and, therefore, it will be carried round it. The same holds good also in respect of the comets, for though they are whirled in a direction parallel to the equator of the sun, yet, the flowing force will at every instant change that direction, and cause them to revolve about his centre. And if any number of planetary bodies be placed at different but sufficient distances from the sun's equator, while he is revolving on his axis, the direction of his axis will be changed, otherwise they could not revolve about his centre or nearly so. And the quantity of alteraations made by the actions of these planetary bodies on the axis of the sun, will be in proportion as the angle made by their courses with the sun's equator.

Since all the planets have a flowing force, tending towards their centres, and decreasing in proportion to the square of the distance, to all distances whatever, it follows, that the sun must have a tendency to the planets, and to every body of the system; as well as they have a tendency toward the sun; and the effect of this tendency will occasion the sun to revolve round the point which is the common centre of all the forces of the sun and planets. This point is found to be within the sun, on account of his vast magnitude compared with that of the planets: for it is computed that the bulk of all

143.-VOL. XII.

the planets, &c., is but the 1-400th
that of the sun.

The planets have not only a tendency toward the sun, but every planet has also a tendency to every other planet of the system, for reasons that have been before explained; and the nearer they are to conjunction, the greater this tendency will be, because then they are nearer to each other. The effects of this tendency are, first, they will approach or be carried nearer to each other as they pass one another, the innermost planet being drawn a little further from the sun, and the outermost drawn a little inward or nearer to the sun. Secondly, As the innermost planet, or that which is nearest to the sun, approaches the outermost, its velocity will be increased until it has passed the point of conjunction, when its velocity will be retarded. Thirdly, The outermost planet before conjunction will be retarded, and after conjunction it will be accelerated in its velocity, and the proportional forces will be as the magnitude of the planets. For instance, suppose that Jupiter is approaching to the heliocentric conjunction of Saturn; here, as Jupiter approaches toward Saturn, the motion of Jupiter will be accelerated and Saturn's motion will be somewhat retarded, and after conjunction the velocity of Jupiter will be retarded and that of Saturn accelerated. But, since the magnitude of Jupiter is greater than that of Saturn, Jupiter must have a more powerful flowing force than Saturn; hence, the action of Jupiter on Saturn would be greater than the action of Saturn on Jupiter.

It is plain from what has been said, that these tendencies of the planets must occasion an irregularity in their motions. But, since they are situated at such vast distances from one another, these disturbances are but small, and this alteration made by them in the system of nature is too little to be perceived even in many ages.

It is a singular instance of the wisdom of the Creator, that the planets are situated at such distances from each other: for if they were nearer they must interfere with one another's motions, and, therefore, occasion many inconveniences to their inhabitants, by making unseasonable alterations in the weather, &c. It is also very wonderful, that the planets Mercury, Venus, the Earth, and Mars, which are comparatively small, move in orbits not far from each other; because their flowing forces cannot greatly disturb their motions; but, the planets Jupiter, Saturn, and the Georgium Sidus, are comparatively more distant, because, being much greater than the former, they would

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Discourse on the Theory of the Planetary System.

occasion greater irregularities in their mo. tions if they were situated nearer to each other.

The whirling forces also must occasion some disturbances in the planetary system, especially when the planets are approaching to conjunction, in which position they will increase or decrease one another's velocity, according to various circumstances, and to their positions. And since all which are known to have a rotary motion, have this force, the united power of it must also have some action on the sun as well as on one another.

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more nearly approaching that of the Earth's equator? The answer to this question is very natural and easy. It must be considered that the Earth and moon are whirled by the motion of the sun in the direction of the plane of the sun's equator nearly, and as the Earth revolves on its axis, the moon will be whirled round it in the plane of the sun's equator, or near thereto: and this consideration proves that one cause constantly operates to keep the Earth and moon in their respective paths.

These irregularities of the moon and planets are such as are observed to take Those primary planets that are attended place by astronomers, and are in accordby satellites, must have a tendency to be ance to the doctrines of Newton on the carried towards their satellites in a similar principles of gravitation and attraction; and way to the sun's tendency to the planets. whether we say that matter is attracted by And as the Earth has but one satellite, both matter, or that matter is carried to matter, will revolve round the common centre of their it is all one, the same effects being produflowing forces, and once in every lunation ced, attraction causing the masses of matter the Earth will make a revolution round to have a tendency to each other in all this point. The satellites of Jupiter, Saturn, | directions. And as matter cannot act upon and the Georgium Sidus will also act upon matter when it does not touch it, but by the one another, as they make their revolutions influence of some interposing medium, it about their primaries in the same way as follows, that there must be a medium. the planets do, and will occasion disturb- that this medium may produce the before ances in one another's motions. mentioned effects, it seems to be necessary, that a continual current of it should flow towards the bodies or masses. Now, since this must be the case in all directions, the fluid medium must be absorbed, and by its elasticity this current may be produced. I should also suppose, that a small force would be sufficient to effect these operations, for it must be considered that the great bodies of the universe have no weight, this being acquired only by the force of this fluid.

As the moon makes her revolution round the Earth, she will be acted upon by the flowing force of the sun, she having a tendency to be carried toward the sun as well as toward the Earth. The consequence of this tendency to the sun is, that the moon's motion in her orbit is irregular. Sometimes she moves at a mean rate, sometimes slower, and at others, faster, according as she is situated in regard to the sun; and, therefore, she will not describe equal areas in equal times. Thus she is accelerated as she passes from the quadrature to the new or full, and retarded as she passes from the new or full to the quarters.

It has before been explained that the moon's orbit is of an elliptical figure, but it must be observed that this tendency of the moon toward the sun causes great vari- | ations in the figure of her orbit; sometimes it is very eccentric, at other times it approaches nearer to a circle. The eccentricity is always greatest in the syzigy, and least when in the quadratures, and variable according to the position of the apogee.

One remarkable property of the moon's orbit deserves particular notice, as it tends to prove the truth of the principles I have advanced, and that is, the greatness of the inclination or angle made by it and the equator. One would naturally ask, if the moon be whirled round the Earth by the Earth's revolution on its axis, why should it take such a cross circuit, and not revolve in a plane

And

This reasoning is similar to that by which we discover the nature and properties of the air, and to deny the existence of such a medium would be the same as to say the wind does not blow when we both hear and feel it, and that there is no air because we cannot see it. When I perceive the trees, &c. shaken by the wind, I know this to be the effect of an adequate cause; and when I see the planets move in their orbits, &c. I infer that these motions are produced by sufficient causes also.

The luminaries have, by reason of the great magnitude of the sun, and the nearness of the moon to the Earth, several influences on our globe. The principal of these are the phenomena of the tides, to which I have already alluded, and which may be further illustrated.

Suppose the Earth to be covered all over to a certain depth with water, then when the moon is situated over any particu lar part of the Earth, it is certain that the

Discourse on the Theory of the Planetary System.

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Sir H. Davy's Ninth Lecture.

though I have been near upon it, and I believe it can be done; to me, there appears to be something analogous between positive and negative electricity, and magnetical attraction and repulsion: perhaps they originate pretty much in one cause. It is highly probable, that the magnetic power is caused by the action of certain fluids, and perhaps the art will sometime be discovered that will make them visible. If the electric fluid had not been rendered visible, it perhaps would have been doubted whether the electric power was caused by a fluid, but every effect must be produced by some adequate cause, and when I see the magnet move a piece of iron without touching it, I know there must be an interposing medium having properties sufficient to do it. The same reasoning holds good, also, with regard to the great bodies of the universe.

THOMAS COOKE.

NOTES ON SIR H. DAVY'S NINTH LECTURE
ON ELECTRO-CHEMISTRY, DELIVERED
IN DUBLIN, 22D NOVEMBER, 1810.
OXYGEN, and oxymuriatic acid are inca-
pable of decomposition.

The first occupies this lecture-the second is to occupy the next.

Priestley and Stahl discovered oxygen at Bristol and Stockholm about the same time. The former called it 'dephlogisticated air,' the latter fire air,' translated into English 'empyreal air.' Priestley made it of red lead; Stahl of manganese. Lavoisier learned it from Priestley, and called it 'oxygen,' founding a system by which he too hastily attributed to an acidifying principle, the property of generating heat and light, in all cases where it is produced, which has been since disproved. These two substances are highly negative in the department of electricity. Oxygen is also made of nitre heated to redness; but the purest oxygen is from hyper-oxymuriate

of potass.

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come the negative electricity of the oxygen -it makes a bright blue lustre.

To confute this deduction made from the foregoing experiment, Sir H. Davy exhibited one of phosphorus in a vessel exhausted of air; it would not burn; which proves that phlogiston is not independent of air.

Favorinus and Mingrelius, two ancient alchymists, first observed the increase of weight received by tin and lead in fusion. This fact made a contradiction in terms, as if taking from added to a metal.

If metals are burned in a stream of oxygen, which is a principle of no phlogiston, they are consumed without residue, like grease thrown into a fire. Place a hard bit of charcoal on a copperplate, and in a hollow of the charcoal place some powder of TIN, set fire to the charcoal, and through a small tube direct a stream of oxygen from a gasometer in a dark room; it burns with a white light. Lead, treated in the same manner, burns peculiarly vivid, with a curling brown smoke over the flame. Copper, burned thus, has a different shade of light, reddish or green. Antimony, treated in this way, burns bright and of various colours. Zinc burns splendidly. And in this manner all metals may be cast on the charcoal and consumed like fuel, leaving only a few impurities, in scoriæ, on the copperplate.

Another contraction to Stahl's system is, the conversion of oxygen gas into carbonic acid gas, by burning charcoal in the retort sealed hermetically; for it is found to be the same weight that it was, previous to the combustion; and if any thing had been dephlogisticated, it must have lost weight. In like manner, a bit of charcoal, and a bit of phosphorus in a closed retort, being ignited by applying a candle flame to the retort under the phosphorus, burns, but the weight of the retort and its contents is undiminished.

When mercury is exposed in common The theory of combustion was asserted air to a heat of 600 degrees of Fahrenby Robert Hoop, in the seventeenth cen- heit's thermometer, it becomes an oxid tury, that the solution of the burning body called minium, which is heavier than the in the air was the same as that of a metal mercury was, although much vapour has in aquafortis.' Becher asserted phlogiston escaped. These facts put down the phloto be a principle generating fire and light, gistic school, and Kirwin gave it up, after which left the residue of combustion de- an able defence. Dr. Black's theory of phlogisticated. Stahl thought he proved this latent heat, proved by undeniable phenoby numberless experiments, the principal menon, removed the difficulty; and Lavoione is to burn bits of sulphur in a small sier, with the same facility as he had apretort of oxygen gas; the gas is proved acidpropriated the discovery of Priestley to his by litmus paper-you can reproduce the (Lavoisier's) system of oxygen, and the sulphur by carbon. The sulphur will not decomposition of common air, from Cavenburn until it is so highly excited as to over- dish, now derived from Dr. Black the

Europe in the Autumn of 1830.