force. The single force of gravitation could give origin only to a rectilineal motion towards the centre, unless the particles were at the same time attracted by some neighbouring patch of nebulous matter. This mistake does not indeed vitiate the author's theory, but it detracts from the simplicity which is one of its chief recommendations, inasmuch as two forces must necessarily be assigned to perform the work which he ascribes to one; or a perfectly arbitrary hypothesis must be assumed of the relative size and collocation of different nebulous masses that their mutual interactions may account for the result.

The rotation having been established, there is generated a tendency in the rotating mass to throw off its outward portions. The least excess of the centrifugal force, thus generated, over the central force, would separate the outer parts of the mass which would be left as a ring round the central body, revolving with the same velocity that the whole mass possessed at the moment of separation. This process might be successively repeated, until the mass had attained its utmost limit of condensation. The excess of the centrifugal force, through which this separation takes place, is supposed to be due to the agency of heat.

The condensation of a nebulous mass around its centre is attended by refrigeration, under which the outer parts acquire a solidity which begins to resist the attractive force. The condensation of the central mass, in the meantime, going on, a point is at length reached at which it shrinks away from its outer crust, which is left, like Saturn's rings, revolving around it.

These rings, unless they are composed of matter perfectly or nearly uniform, would necessarily break into several masses, the largest one of which would attract the others into itself. The whole mass would then take a spherical form, and become a planet revolving round the sun, and upon its own axis. The rotatory motion of this planet might in turn throw off one or more rings, which by a similar process would become transformed into satellites, having a three-fold motion on their own axes, around the planet, and with it around the sun.

It

Such was the genesis of our solar system, which shows in the different bodies composing it, all the variations, with one exception, which this law of construction was capable of producing. contains some planets, which when thrown off were too much solidified, or from other circumstances so conditioned that they threw off no outer crust, and are therefore without satellites, while others are attended by these secondary products of the centrifugal force, in varying numbers. And again, in the space between Mars and Jupiter, where Kepler, listening only to the harmonies of the system, which, as he expresses it," he had stolen from the golden vases of the Egyptians," had prophesied the discovery of a planet, we have in the four asteroids an instance, which might have been expected sometimes to occur, in which the different portions into which

the planetary ring broke up were so situated that no one of them absorbed the others, and hence each became a separate minor planet. In the two rings of Saturn we are also presented with a case of what might rarely happen, in which the particles of matter composing the separated crust were so uniform, that it remained entire instead of breaking up into satellites. These varieties, inasmuch as they lie within the possibilities of the hypothesis, are deemed a confirmation of its truth. So, also, another apparently anomalous construction, that of solar systems embracing two or more suns, many of which are visible in our firmament, is supposed to render support to the hypothesis which at first sight it seems to threaten. Some of the double stars are found by careful observation to revolve round each other in ellipses, and hence it is fair to infer that they all do. A system of this kind would therefore be generated, precisely like ours, if there were given at the outset two or more nuclei, instead of one, in the diffused nebulous mass.

At this point the author again stumbles in referring the genesis of the motions in such a system to the same law which sometimes produces two or more neighbouring whirlpool dimples upon the face of a river. "These fantastic eddies, which the musing poet will sometimes watch abstractedly for an hour, little thinking of the law which produces and connects them, are an illustration of the wonders of binary and ternary solar systems." We must be permitted to say that the musing poet is much more profitably employed upon the whirling dance of these fantastic eddies, than the thinking philosopher, unless he thinks to better purpose. The one, in the subjective law which determines his musing, reaches a reality, while the other, in his scientific search after the actual law of production, finds only a shadow.*

This error of the author, however, affects his hypothesis only so far as its simplicity is concerned. He has, beyond all question, erred in supposing that he could generate the motions of a solar system, whether with one or more suns, simply by postulating in

* Another amusing illustration of the carelessness of the author, to call it by no harsher name, is found on p. 24, where he informs us that "the tear that falls from childhood's cheek is globular, through the efficacy of the same law of mutual attraction of particles which made the sun and planets round." Why did he not add that the soap-bubble preserved its spherical form from the action of the same cause which determines Saturn's ring? The attraction of gravitation has as much to do in the case of the bubble as of the tear, that is, it has nothing to do with determining the peculiar form of either, that form being due to the superficial action of the particles. Familiar illustrations of ultimate scientific principles are dangerous things in the hands of one who allows himself to think and speak loosely.

We find on p. 29 a still grosser error. "A chemist, we are told, can reckon with considerable precision what additional amount of heat would be required to vaporise all the water of our globe-how much more to disengage the oxygen which is diffused in nearly a proportion of one-half through its solids; and finally how much more would be required to cause the whole to become vaporiform, which we may consider equivalent to its being restored to its original nebulous state." This confusion of vapour with nebulous matter is a blunder too gross to have escaped a mind accustomed to accurate habits of thinking. The conception which the necessities of the hypothesis compels us to form of nebulous matter is as unlike to vapour, as it is to granite.

addition to the other conditions, the property of gravitation in the particles of nebulous matter. His postulates, thus far, are diffused masses of nebulous matter filling immense portions of space; this matter intensely heated and endowed with a tendency to throw off its heat under the process of condensation; the origination, in some unknown way, of nuclei or centres of condensation at different points in these nebulous masses; and, lastly, the existence of a property in virtue of which the particles of this matter mutually attract each other in the inverse ratio of the square of the distance. These postulates, though by no means distinctly put forth, are all embraced in the hypothesis, and it is therefore a matter of comparatively small moment that the error which we have pointed out renders an additional one necessary. But it tends to weaken our confidence in one who offers himself as our guide in tracing out the vestiges of creation, when we find him stumbling at the outset among the first elementary principles of physical science. Nor is he always consistent with himself. It has been seen that the hypothesis which he is expounding demands that the nebulous mass should be accompanied by a process of cooling, so that Uranus, the outermost planet, was formed when the heat of the matter composing our system was at the greatest, and Mercury when it was at the least. This, the author supposes, will account for the decreasing specific gravity of the planets as we recede from the sun. The outer planets having been thrown off when, in consequence of the greater heat of the mass, its particles were more diffused, would of necessity be lighter than those which were subsequently detached. The greater heat, too, which these distant planets retain, he thinks, may be sufficient to compensate for the smallness of the portion which they receive from the sun's rays. And yet in immediate connexion with this exposition he asks, "where, meanwhile, is the heat once diffused through the system, over and above what remains in the planets? May we not rationally presume it to have gone to constitute that luminous envelope of the sun, in which his warmth-giving power is now held to reside? It could not be destroyed-it cannot be supposed to have gone off into space-it must have simply been reserved to constitute at the last, a means of sustaining the many operations of which the planets were destined to be the theatre." We cannot understand why this heat may not be supposed to have passed off into space and still less can we comprehend how it can have passed to the sun, when, by the hypothesis, the genesis of the sun, with its attendant planets and satellites, is to be explained by the continual escape of heat from the contracting mass. We see signalized here the extreme, unscientific haste with which the author frequently leaps to his conclusions. In the first instance he asks, whether we may not presume that the escaped heat has gone to constitute the luminous atmosphere of the sun, the proper answer to which would be, certainly not, unless we presume at the same time that the whole ground-work of the

hypothesis, as expounded up to the very sentence preceding this, has disappeared. And then he passes, without assigning any reason except the statement of two alternatives, which are by no means exhaustive of the possibilities of the case, to the peremptory conclusion, that this heat must have been reserved to constitute a magazine at the centre for the use of the system. But how reserved, and where? and how gathered around the sun after the cooling process has reached its limit?

A like gross inconsistency appears in his attempt to explain the apparent condition of the moon. The characteristics of the moon's surface forbid the idea that it is at present a theatre of life like the earth, but the author warns us against drawing the inference that it never can become so. "The moon may be only in the earlier stage of the progress through which the earth has already gone. Seas may yet fill the profound hollows of the surface-an atmosphere may spread over the whole." The rugged state of the moon is thus to be explained by the earlier stage of growth at which this body now is as compared with the earth. But it has been seen that the hypothesis requires that the moon should have been thrown off long before the earth had contracted to its present dimensions and on the page but one preceding this we find it stated that "the time intervening between the formation of the moon and the earth's diminution to its present size was probably one of those vast sums in which astronomy deals so largely, but which the mind altogether fails to grasp." In accounting for the invariable size and temperature of the earth, he again betrays his ignorance of the elementary truths of physical science. "The central heat," he says, "has for ages reached a fixed point, at which it will probably remain for ever, as the non-conducting quality of the cool crust absolutely prevents it from suffering any diminution." It is true that there is no process of shrinking now going on in our globe, which we have any means of detecting. A very slight diminution of the diameter would affect the diurnal revolution of our globe, and it is demonstrable that the time of this revolution has not varied the three hundredth part of a second for the last two thousand years. And yet the hypothesis of the author would seem to require that the continual escape of heat from the central fires of the earth should lead to a still further condensation

of its mass. This difficulty he meets, with sufficient boldness, by denying any degree of conducting power to the earth's crust, so that all the heat which existed within when the surface acquired, ages ago, this marvellous power, has been retained ever since, and is now imprisoned beyond all hope of escape. There cannot be many of our readers who need the information that this non-conducting quality of the crust is a pure fiction. If the crust be impervious to heat, why is it that after we have reached, at the depth of some sixty or eighty feet, the region of invariable temperature, we find the heat increasing upon us with every foot that we descend? It is indeed true that the crust has a very low conducting

power. Only a few years since Mairan and Bailly agreed in making the amount of heat received from the interior of the globe to be, in summer, twenty-nine times, and in winter, four hundred times. that received from the sun; a calculation which gave promise of a speedy congelation. from the rapid dissipation of the internal heat. But Baron Fourier succeeded in proving that the thermometric effect of the central heat upon the surface of the globe did not exceed the thirtieth part of a degree of the centigrade thermometer. The author of the Vestiges of Creation, however, is the first philosopher who has ventured to affirm that there is absolutely no escape of heat from the interior, and to assign as the reason the non-conducting quality of the crust. If the interior of the earth is, as many considerations would lead us to suppose, in an incandescent state, there can be no doubt that a portion, however small, of its heat must escape and fly off into space. The unshrinking dimensions of the earth, which would seem to be in opposition to this conclusion, might be better accounted for by supposing that the contraction in some of the elements of the mass, due to this loss of heat, was balanced by an equivalent expansion of others in passing from a liquid to a solid state; or in many other ways, rather than by denying that any heat is lost, and assigning for it a purely fanciful reason.

It ought to be stated, in justice to Laplace, that the author of this work has, in many respects, misapprehended his nebular hypothesis; and that objections therefore may be justly taken against his statement of it, which would not lie against it in the form given to it by its proposer. The method by which he explains the shelling off of planets and satellites, through the hardening of the outer surface and the resistance thus opposed to the attractive force of the interior mass, is absurd upon its very face, and utterly insufficient for the explanation of the facts of the case. Admitting the action of the principles stated as ruling the case, a spherical shell would be separated, and not an annular ring. The author confounds these together, speaking in one sentence of the separation of the solidifying crust," and in the next terming this crust "a detached ring" not only without any explanation of the manner in which the spherical shell has become transformed into a circular band, but apparently without any idea that he is speaking of two very different things. Into this difficulty he has been betrayed by introducing the comparative solidification of the crust as the cause of the separation. This separation is effected, according to Laplace's hypothesis, not by the hardening of the surface, but by the accumulation of matter in the equatorial region. In a fluid body revolving upon an axis, the matter would be heaped up at the equator; and the centrifugal force of the outer portion of the protruding belt thus formed being greater than of any other portion of the mass, a point would at length be reached at which there would be an exact equilibrium between this force and the central attraction. An annular ring would then be separated, which