tre of gravity had at any one time, it is demonstrable that it must keep unaltered, except by the attraction of the fixed stars; and it is millions to one against there having been no motion whatever of this centre at the time when the system received its organization. And if there be any attraction from the fixed stars, however little, some motion must be produced. Centuries of close observation on double stars may, and probably will, detect the motion of our system. All that can be said up to the present time is, that, be it what it may, it is exceedingly small, compared with the distance of our System from these stars.

The next question may be, is there any evidence in our System of any secondary law of formation, indicating a connection between the mode of creation of one planet and another. The will and power of the Creator are the final causes both of the initiation and maintenance of this vast machine; but in the latter there are visible secondary laws, that of attraction, for instance: were there any in the former? Attempts at investigation on this point have been frequently considered atheistical; a foolish notion arising out of those views to which we have alluded in MOTION, p. 452. Those who can only think of the Creator and forget the Maintainer, and who virtually separate the office of the latter, and give it to the laws of nature,' may reasonably fear that they would have to give up also the former office to the laws of creation,' if such were found; which would be (but owing only to their own interpretation of the manner in which the world continues to exist) a renunciation of the idea of Deity in the contemplation of the manner in which it began to exist. But to those who keep constantly in view the fact which no modern theist disputes, that the same power which created continues to create in preserving, and that the laws of nature' are only expressions of the manner in which this preservation is seen to act, will look upon the laws of creation to be as simple and natural an object of philosophical inquiry as those of the ascent of sap in a plant, or of the revolution of a planet. The proper reply to a charge of atheism brought against those who investigate any mode of action of the Creator of the universe, at any past time, is the retort of semi-atheism against those who make it. Many speculations have been made upon the formation of the several planets, but none which has any appearance of connecting the phenomena of one planet with those of another, except by Laplace (Système du Monde, vol. ii., note 7), in what has been called the nebular hypothesis. This conjectural theory, which is well worthy of attention, never received any particular notice, to our knowledge, from any writer in this country, until Mr. Whewell's Astronomy and General Physics,' the third of the Bridgewater Treatises, appeared, in which it is announced that the nebular theory was ushered in with expressions which showed Laplace to be a professor of atheism. What Laplace really thought on these subjects, as we have said before [LAPLACE], we do not know, nor would it really matter if he were what he was represented to have been; for a conjecture may be ingenious, and a theory sound in its details, even though its author made it stand in the place of a Creator. But considering the collateral associations connected with such a charge, it will be well to examine into the fact whether there was any such announcement; and to do this fairly, we must quote both Mr. Whewell and Laplace. The former says, We have referred to Laplace as a profound mathematician, who has strongly expressed the opinion that the arrangement by which the stability of the Solar System is secured is not the work of chance; that "a primitive cause has directed the planetary motions." This author however, having arrived, as we have done, at this conviction, does not draw from it the conclusion which has appeared to us so irresistible, that "the admirable arrangement of the Solar System eannot but be the work of an intelligent and most powerful Being." He quotes these expressions, which are those of Newton, and points at them as instances where that great philosopher had deviated from the method of true philosophy. He himself proposes an hypothesis concerning the nature of the primitive cause, of which he conceives the existence to be thus probable.'

Here are two assertions:-1, That it is the doctrine of an intelligent Creator which Laplace points at' as a deviation from true philosophy; 2, That Laplace proposes his nebular hypothesis as a primitive cause. We pay a writer of Mr. Whewell's character the compliment of inserting here matter which would more appropriately appear in a review of his work and we deny that Laplace has been well

described in either assertion. Our object is to clear the nebular hypothesis from the unphilosophical character with which its first appearance is thus presented, and by no means to uphold the moral dignity of Laplace. Until the biting facts connected with his treatment of his benefactor [Vol. xiii., p. 325] are answered or explained, that great mathematician must be called a time-server; and we suspect that his 'Système du Monde' only treats the intelligent Creator whom his mind acknowledged, in the same manner as he afterwards treated Napoleon. It was published in 1796, a period which would well explain the mere suppression of all allusion to the Supreme Being: and one of these things must be true; either Laplace was what Mr. Whewell styles him, or he had not the courage to declare himself otherwise in his age and country. But what we have here to do with is the assertion that he did more-that he attacked the doctrine of a Supreme Being. His words are as follows, the passages to which we wish to draw attention being in Italics :-'I cannot here help observing how much Newton has departed on this point from the method which he elsewhere so happily applied. After the publication of his discoveries, this great geometer, abandoning himself to speculations of another nature, inquired into the motives which made the Author of nature give to the Solar System the constitution which we have described.' Laplace then quotes Newton's Scholium (PRINCIPIA, pp. 10, 11, where we have translated the whole) thus: And all these regular motions have no origin in mechanical causes,* &c. &c. down to all parts of the heavens.' He then further quotes, This most elegant group, &c. can only arise from the design and government of a powerful and intelligent Being.' He (Laplace) continues thus, speaking, so far as the mere notion of a Supreme Being is concerned, rather in approbation: He repeats the same thought at the end of his Optics, in which he would have been still more confirmed if he had known what I have demonstrated, namely, that the arrangement of the planets and satellites is precisely that which makes a certain provision for their stability. "Blind destiny," says Newton, “can never make the planets move thus with such small irregularities, which appear to come from the mutual action of the planets and comets, and which will probably become greater and greater in the course of time, until at last the System will again require its author to put it in order." But,' proceeds Laplace, may not this arrangement of the planets be itself a consequence of the laws of motion, and may not the Supreme Intelligence, which Newton makes to interfere, have already made it depend upon a more general law? Are we to affirm that the [unlimited] preservation of the Solar System is a part of the intentions of the Author of nature?' This we should sum up as follows: Laplace charges Newton with a departure from philosophical principles in-1, Speculating on the motives of the Creator; 2, Assuming the probability that his works would not last his time without his own supernatural interference; 3, Assuming that he intended to preserve the Solar System for ever. But Mr. Whewell singles out only one part of Laplace's quotation, and without paying any attention to the remarks which explain his meaning, declares that Laplace pointed at' Newton's declaration of belief in God as a piece of bad philosophy; whereas this part of his quotation is only followed by the remark how much stronger he himself (Laplace) had been able to make the sort of evidence on which Newton rested; and the sentence selected by Mr. Whewell as pointed at,' coupled with the remark specially made on that sentence, has rather the appearance of being pointed at with approbation. With regard to the assertion that Laplace propounded the nebular theory as a primitive cause, it is true that he did so in his own sense of the words. Mr. Whewell means by primitive cause a first cause, as those words are usually understood: and he asks (and the question would have been much to the purpose if Laplace had really meant the same thing as himself by the words primitive cause), Was man, with his thought and feeling, his powers and hopes, his will and conscience, also produced as an ultimate result of the condensation of the solar atmosphere? But Laplace speaks as follows: Quelle est cette ccuse primitive? J'exposerai sur celà, dans la note qui termine cette ouvrage, une hypothèse,' &c. And in the very first words of this note

Laplace evidently thought that by mechanical causes Newton meant what we now call second causes. See the reference just made.

Newton's Scholium does not seem to us to do any such thing; but that is not the question. Laplace's approval or disapproval is of course to be applied to his own interpretation of Newton's meaning, not to ours.

we find, 'On a, pour remonter à la cause des mouvemens primitifs du système planetaire,' &c. This then is what Laplace understood by primitive cause, a cause of the primitive motions;-an improper use of language, if the reader pleases; but when a man puts his own meaning on his own words, no one has a right to fix the consequences of another meaning upon him.

the mass.

We now proceed to the nebular theory, which is a conjecture proposed with much doubt by Laplace, as a possible explanation of the manner in which the motions of the several planets obtained those remarkable resemblances which are found to subsist, without making the inquiry extend to anything except their motions. All the planets move in one direction round the sun, and their satellites move in the same direction round themselves; those that are known to revolve round their axes (and the contrary has been proved of no one of them) also revolve in the same direction, and their equators are not much inclined to their orbits. The excentricities of the planets and satellites are in no case very large, and generally very small; and the inclinations of their orbits to one another are generally small. Many nebulæ in the heavens appear, when examined, to consist of a bright nucleus surrounded by nebulous matter; in others it is found that the apparently nebulous matter consists of stars. This gave Laplace the idea that our System might originally, that is, previously to the establishment of its present order, have been a large nebula of which the sun was at the centre. Imagine a large nebulous mass in a state of revolution, with a solid or at least less nebulous centre, round which it revolves: call this central nucleus the sun. Assume the ordinary laws of matter to be true of this nebulous mass; and also that it extends as far as such an atmosphere can do; namely, until the attraction of the whole upon particles at the equator is equal to the centrifugal force of those particles. If condensation should begin to take place, arising from loss of heat, the mass would revolve more and more rapidly as it was condensed into less and less space; but it does not follow that the equatorial particles would fall in towards the centre: they are balanced by the equality of the centripetal and centrifugal forces; and might form a ring round the rest of If the process were conducted with great regularity, this ring and the mass of vapour might undergo continual condensation together, until the increasing velocity of rotation prevented the formation of the ring from continuing. The departures from complete regularity which might exist in the mass might cause disturbances in the formation of the rings, which might end in there being one or more (not many) permanently revolving round the rest of the mass condensed into a solid body, in the manner of Saturn and its rings. Such regular formation however might be rarely continued long enough; and if the rings got broken, each ring would become several masses, which would revolve nearly at the same distance, and nearly with the same velocity: such a result is seen in the four small planets. But as, generally speaking, these masses would, by irregularities in their velocities, be combined into one at last, each broken ring would form a new nebulous mass, revolving round the diminished central nucleus: and if a number of such masses were formed, those nearer to the central mass would move with the greater velocity, and would be both smaller and denser than the external ones: the first circumstance certainly, the second and third most probably. Again, each mass would have a motion of revolution in the same direction [MOTION, DIRECTION OF] as the motion round the primary; for when the ring becomes broken, its internal parts have a somewhat more rapid motion than the external ones, which would give the motion of rotation noticed. And the rotations thus created in the internal masses would probably be greater than those in the external masses. The orbits of the masses would necessarily be nearly circular, and not much inclined to each other: but for irregularities, quite circular, and in the same plane. In each of the nebulous masses, thus detached and revolving, condensation might again give rings or satellites or both; but in all probability the external masses would get more satellites than the internal ones: the orbits of the satellites must be also nearly circular, and not much inclined. All the preceding circumstances, both those which • If any number of masses, capable of cohering, revolve in orbits so near to one another that they must cohere when they come to their minimum dis tance, nothing but an absolute and mathematical equality in their mean velocities can keep them permanently asunder; the smallest inequality must at last bring them all together,

are certain and those which are probable (Laplace confined himself to the former), are actually existing in the Solar System; consequently this hypothesis, though subject to serious difficulties, deserves attentive consideration, as often as any new knowledge of the constituent parts of our system shall render a reference to it likely to produce evidence on one side or the other. As a substitute for intelligent creative power, if such a thing were intended, it would do no better than any other; for, as Mr. Whewell observes, a man with will, power, and conscience, cannot be admitted to be a necessary consequence of the cooling of a nebulous atmosphere. Nevertheless, as exhibiting a possible mode in which the Creator of mind and matter made the laws of formation resemble those of continuation, as far as the motions of the system are concerned, this hypothesis is strikingly explicative of what we really see. But even if we were to take it to be a true explanation, it would only be one step of the ascent, and the next question would be, what higher process distributed the parts of this nebulous mass in such a manner as to place those outermost which were fit to form a planet so distant from the source of light and heat as Uranus, and to support the appropriate forms of animal and vegetable life which analogy would induce us to suppose must exist there.

The history of astronomy teaches us that the system in which we live has not undergone any apparent change for more than 2000 years; and, on inquiring into the connection which exists between one planet and another, or the laws of gravitation, it is found that so far as their mutual actions are concerned, there is no reason why any change ever should take place. If the central body were the only one which attracted the rest, and as long as the laws of matter remained unaltered, it is certain that nothing could alter the revolutions of a system of planets, unless two orbits intersected, and the planets of those orbits happened to come to the intersecting part at the same time, and to strike each other. But the planets are subject to the action of each other as well as to that of the sun, and no instant elapses without every orbit undergoing a slight change from every one of the planets of the other orbits. Jupiter alone produces on the earth's orbit in one year more change than we have any right to say all the comets put together would do in a hundred. And yet the system not only continues without any sensible change, but, one circumstance alone excepted, to which we shall presently allude, is demonstrably formed to continue for a most enormous length of time, unless some new action should arise, or some external cause begin to operate. As it is sometimes stated that a complete mathematical demonstration has been given of the eternal stability of the Solar System, so far as the mutual actions of its parts are concerned-an assertion which is altogether incorrect--it may be worth while to enter a little on the details of this subject.

The disturbing forces of the planets on each other cannot have their effects calculated all at once; but each force must be divided into an infinite series of terms, the first of which contains all the terms of the first dimension, the second all those of the second, and so on. Of all these terms each is much less in its effect than the preceding; so that in fact the first two dimensions are all that produce any sensible effect in any time which it is worth while to consider. Occasionally it happens that terms of the third and fourth dimensions have been required to be used, but almost all the sensible perturbations of the system depend on terms of the first two orders. As far as any effects arising from such terms are concerned, Lagrange and Poisson are admitted on all hands to have demonstrated the stability of the Solar System: and considering the nature of the process employed, and there being no appearance of any circumstance which looks likely to lead to a different result in any of the remaining terms of the disturbing forces, it may be highly probable that a further investigation would show the same thing, if all the dimensions of the disturbing forces were employed. Sir J. Lubbock (Phil. Mag, February, 1831) has pointed out the forms which further investigation would apparently produce, and which would (unless a detailed investigation should lead to something not discoverable a priori) bear out as certain what we have just stated to be probable. But though all the presumptions lie on the side of those who would assert the proposition absolutely of all dimensions of the disturbing force, it is not yet time to say that it is a certain mathematical consequence of the theory of gravitation,

When the effects of preturbation are examined, as far as the second dimension of the disturbing force, it appears that the immense mass of the sun compared with that of any planet, the great distance of the planets from each other as compared with their amounts of departure from spherical form, the small excentricities and inclinations of their orbits, and their motions being all in one direction, give the following mathematical consequences of the law of attraction:First, the longest or major axes of the planets' orbits are not subject to any slow variations of very long period; all their variations being excessively small, and soon destroyed by the production of contrary variations. It is very often stated that the major axes are subject to no variation; this is to be understood only of secular variation (or of very long period). One year is not precisely the same as another to any fraction of a second; but the average year of one long period is precisely the same as that of another; or at least the mean years of the two periods become more nearly equal the longer the periods are made. But the excentricities and inclinations are subject to long periodic alterations, the times of their recurrences not being exactly settled, from the difficulty of their determination. How then is it known that they are periodic? For instance, the excentricity of the Earth's orbit is subject to a yearly diminution of 00004, its value in 1801 being 017. Had this diminution been an increase, as it is in Mercury and Jupiter, it might à priori appear possible that this increase should continue until the orbit (preserving the same major axis) should be so elongated that the ultimate approach to and recession from the sun should give our planet the alternate climates of Mercury and Mars, and thus no doubt destroy it as the abode of beings constituted like ourselves. It is found however that the following relation must exist:-If at any one moment the square of the excentricity of each planet be multiplied by its mass and the square root of its mean distance from the sun (represented in numbers), the sum of all these products must be the same as it was at any moment past, or will be at any moment future. And if in each product the tangent of the inclination to a fixed plane be substituted for the excentricity, the resulting equation is true. From such relations as these, and others connected with them, it is shown that so far as the mutual actions of the planets are concerned, no one excentricity nor inclination can increase indefinitely, but all their changes must be periodic, and confined within rather small limits. The approach of the ecliptic to the equator, for instance, which amounts to about half a second in a year (and which leads speculators sometimes to talk about a past time when the ecliptic passed through the pole, and a future time when it will coincide with the equator), must stop long before the ecliptic reaches the equator, and attain a minimum inclination, after which the two will begin to separate; the whole oscillation being less than three degrees. The whole result is summed up thus: As far as terms of the second order (inclusive) in the disturbing forces, and as long as only the mutual attractions of the planets act, there is a mathematical certainty that the Solar System will remain in its present state, the elements of the different orbits oscillating about certain mean values, from which they are never very distant: except only the longitudes of the nodes and perihelia, which change with velocities which are always very near to a certain mean velocities. The probability is very small that the higher dimensions of the disturbing forces would affect this result, and certainly only in a length of time to which the longest periods known are trifling in comparison.

This last point however is of the less importance, since it has become highly probable, within the last few years, that an external cause does exist, which must, unless there be a counteracting force of which we know nothing, in time cause the destruction of the System. If the planets move in any medium which resists their motions, however little, the consequence must be a gradual diminution of their mean distances from the sun, and a gradual increase of their velocities, ending in their absolutely falling into the sun. For the presumption in favour of the actual existence of such a resisting medium, see COMET, p. 394. This retarding agent seems to show a rapid effect upon so attenuated a mass as Encke's comet, though thousands of years have elapsed without its producing any sensible effect upon the planets. Little as it may concern us directly, these speculations have an interest, both as to the glimpse they give of the possible destiny of our System, and from their association with the history of past and the hope of P. C., No. 1384,

future discovery. It is to be remembered that no science has drawn out so much of mathematical talent, or indirectly excited such an influence upon other branches of physical research, as the application of the theory of gravitation to the development of the planetary motions.

For more detail upon the subject, in a popular manner, the English reader may consult Sir John Herschel's Treatise on Astronomy,' in the Cabinet Cyclopædia, or Mrs. Somerville's Treatise on the Physical Sciences.'

SOLA'RIO, ANTONIO DE, called 'Il Zingaro,' or the Gipsy, was born in 1382, at Chivita, in the Abruzzi, ac cording to Dominici (Vite de' Pittori Napolitani), but others have contended that he was a Venetian. He was a gipsy by birth, and in his youth was a sort of itinerant blacksmith. He was not a mere tinker, a mender of kettles and saucepans, for he is said to have been admitted into the house of the painter Colantonio del Fiore at Naples, on account of his skill in making implements of iron. Nearly the same story is related of Solario as of Matsys, the blacksmith of Antwerp. [MATSYS.] Solario fell in love with the daughter of Colantonio, and she fell in love with him. Solario made proposals, but Colantonio said that he would never consent that his daughter should marry any one but a painter of reputation at least equal to his own. The gipsey was not to be thus got rid of; he asked to be allowed ten years to study the art, and Colantonio, to satisfy his daughter, assented. Solario became a pupil of Lippo Dalmasi at Bologna, with whom he remained six or seven years, and afterwards travelled through the chief towns of Italy in order to study the works of other masters. In rather more than nine years he returned in disguise to Naples, and having presented to the queen of Naples a picture of the Virgin, with the infant Jesus crowned by angels, and also been permitted to paint a portrait of the queen, Colantonio was then invited to view the productions of the unknown artist, of which he expressed the highest admiration. Solario then discovered himself, and soon afterwards became the son-in-law of Colantonio. His reputation was immediately established, and he was much employed, especially at Naples, in painting altar-pieces, and in decorating the walls of convents and other religious houses with frescoes. In the fine expression of his heads, and in the richness and harmony of his colouring, he has been compared to Titian. He is also praised for the graceful action of his figures, but is said to be defective in the drawing of the hands and feet. Solario was also distinguished as an illuminator of manuscripts, especially Bibles. He died in 1455. Vasari has not included Solario in his 'Lives.'

(Dominici, Vite de' Pittori Napolitani; Moschini, Memorie della Vita di Antonio de Solario, detto Il Zingaro, Pittore Viniziano, Venezia, 1828.)

is

SOLA'RIUM. [TROCHIDE]

SOLDA'NIA. [FORAMINIFERA, vol. x., p. 348.] SOLDERING, according to Dr. Ure (Dict. of Arts, &c.), the process of uniting the surfaces of metals, by the intervention of a more fusible metal, which, being melted upon each surface, serves, partly by chemical attraction, and partly by cohesive force, to bind them together.' In accordance with this, which is the ordinary acceptation of the word soldering, a solder may be defined as a metallic cement employed to unite, by being fused between them, two pieces of metal. Such an explanation however, though correct in most cases, does not apply to every kind of soldering; a process having been recently introduced by which pieces of metal may be perfectly united without the interposition of solder.

In the ordinary mode of soldering, the alloy used as a solder must be more fusible than the metal or metals which are to be united, and must have a strong affinity for them. The solder usually contains a large proportion of the metal to which it is to be applied, in combination with some more easily fusible metals. To insure perfect melallic union between the solder and the surfaces to which it is applied, it is essential that they be made perfectly clean and free from oxide, and that the atmosphere be excluded during the operation, in order to prevent the formation of any oxide while the process is going on. This is effected in various ways, but most commonly by the use of borax, sal ammoniac, or rosin, either mixed with the solder or applied to the surfaces to be joined. Mr. Thomas Spencer, of Liverpool, has recently made some interesting experiments, the results of which are given in a paper On the Theory and Practice of Soldering Metals,' which was read before the Liverpool PolyVOL. XXII.-2 D