and starts for ever, and be as powerful a million of years hence as in those incalculably ancient times when our Scottish gneiss was in the forming. Accepting the theory of Sir Humphrey Davy, of an unoxidized metallic nucleus of the globe, capable of being oxidized all around its periphery by the percolation of water, and of evolving heat enough in the process to melt the surrounding rocks, he thus provides plutonic, metamorphic, volcanic agencies; and whereas Sir Humphrey Davy held, that when a thick crust of oxide had once formed in this way, it served to shut out the water, and the chemical action became in consequence more and more languid, till it altogether ceased, Sir Charles finds, in another but harmonizing theory, an expedient for re-invigorating the slumbering plutonic forces, and thus, after a period of repose, renewing their activity. The oxygen of the water is, of course, the oxidizing agent; but water also contains hydrogen, and hydrogen is a de-oxidizing agent. 'When the oxidizing process was going on,' says Sir Charles, 'much hydrogen would of necessity be evolved: it would permeate the crust of the earth, and be stored up for ages in fissures and caverns; and whenever it happened to come in contact with the metallic oxides at a high temperature, the reduction of these oxides would be the necessary result.' And we have thus a circle of forces,—oxidization of the metallic basis to evolve the plutonic agencies, and de-oxidization of the oxides to produce the metallic basis again. The process would somewhat resemble that on which the movement of the steam-engine depends, and in which water is first expanded into steam, and then the steam in turn condensed into water, and thus the action of the engine kept up.

Now, I need not here say how thoroughly I respect the judgment and admire the genius of Sir Charles Lyell,-one of the greatest of geologists, and a man of whom Scotland may well be proud; nor need I say how much of pleasure

and instruction I owe to the rich and eloquent writings of Professor Nichol. But, like Job's younger friend, I too must take the liberty of showing forth my opinion, and of giving expression to a conviction, on grounds of which my audience must judge, that both Sir Charles and the Professor have suffered the re-action wave to carry them too far.

Mr. Charles M'Laren, in a popular digest of Mr. Hopkins' deductions, which first appeared, if I remember aright, in the Scotsman newspaper, and then in Jameson's Philosophical Journal, referred, with his characteristic caution, to the narrowness of the base on which they rested. 'Mr. Hopkins' conclusion no doubt rests,' he said, 'on a narrow enough basis. It is somewhat like an estimate of the distance of the stars deduced from a difference of one or two seconds in their apparent position,-a difference scarcely distinguishable from errors of observation.' Let us, however, waive the doubt implied in this remark, however important we may deem it, and grant, for the argument's sake, that the base is sufficiently broad for the superstructure erected upon it. Let us freely grant, after first availing ourselves of Mr. M'Laren's protest, and placing it on record, that that equatorial ring, thirteen miles in thickness, which, by disturbing the balance of the earth, is the cause of the phenomena of Precession and Nutation, must be attached to a consolidated crust of at least a thousand miles in thickness, in order to account for the extreme slowness of the peculiar movement which it induces. But let us then inquire how it happens that this equatorial ring at all exists. If our earth was always the stiff, rigid, unyielding mass that it is now, a huge metallic ball, bearing, like the rusty ball of a cannon, its crust of oxide,-how comes it that its form so entirely belies its history? Its form tells that it also, like the cannon-ball, was once in a viscid state, and that its diurnal motion on its axis, when in this state of viscidity, elongated it, through the operation of a well-known law, at

the equator, and flattened it at the poles, and made it altogether the oblate spheroid which all experience demonstrates it to be. It may be urged, however, that this form of our planet, which seems to speak so unequivocally of law, may, after all, be but accident. If so, it must be singular. What say the other planets? Of these, the form of three may be at least approximately, and that of one exactly, ascertained. Venus, Mars, Saturn, are all, like our earth, oblate spheroids, flattened at their poles, and elongated at their equators. Their substance must have been spun out by their rotatory motion in exactly the line in which, as in the earth, that motion is greatest. But while we can only approximately determine the values of the equatorial and polar diameters of these three planets, in one great planet, Jupiter, we can ascertain them scarce less exactly than in our own earth; we can gauge, and measure, and fix the proportions which his equatorial ring bears to his general mass. With a diameter about eleven times larger than that of our planet, and rotating on his axis in less than half the time, the motion of the surface at his equator must be more than twenty times greater than that of the earth's equatorial surface, and his equatorial ring ought, even in proportion to his huge bulk, to be more than twenty times as massive. And what is the fact? While the thickness of the equatorial ring of the earth is only equal to about one threehundredth part of the earth's diameter, the equatorial ring of Jupiter is equal to about the one fourteenth or fifteenth part of his diameter. It is, as the integrity of the law demands, more than twenty times greater in proportion to his mass than the earth's equatorial ring, and absolutely more than two thousand times greater. Here, then, is demonstration that the oblate sphericity of the earth is a consequence of the earth's diurnal motion on its axis; nor is it possible that it could have received this form when in a solid state. A glass ball made to revolve on a spindle when in

a state of viscidity elongates equatorially, and flattens at its poles; but if allowed to cool in its original form as a sphere, it retains its perfect sphericity without change, let us whirl it as rapidly as we may; and no mechanic ever dreams of increasing the disk of a grindstone simply by turning it round. The earth, then, when it assumed its present form, could not have been a solidified mass, like the glass sphere when cooled down, or like the grindstone.

But is it not possible, it may be asked, that the diurnal motion may so act on the depositions taking place in the sea and forming sedimentary rock, or on a region of igneous action interposed between the oxidized crust of the earth and its solid metallic nucleus, and forming plutonic or igneous rock, is it not possible that, in the course of vastlyextended periods, the earth may have taken its form under the influence of the motion exerted on sedimentary deposition and plutonic intrusion and upheaval? Nay, what, we ask in reply, are the facts? Does the diurnal motion exercise any influence, even the slightest, on deposition or plutonic intrusion? The laws of deposition are few, simple, and well known. The denuding and transporting agencies are floods, tides, waves, icebergs. The sea has its currents, the land its rivers; but while some of these flow from the poles towards the equator, others flow from the equator towards the poles, uninfluenced by the rotatory motion; and the vast depth and extent of the equatorial seas show that the ratio of deposition is not greater in them than in the seas of the temperate regions. We have, indeed, in the arctic and antarctic currents, and the icebergs which they bear, agents of denudation and transport permanent in the present state of things, which bring detrital matter from the higher towards the lower latitudes; but they stop far short of the tropics; they have no connexion with the rotatory motion; and their influence on the form of the earth must be infinitely slight; nay, even were the case otherwise, instead of tending

to the formation of an equatorial ring, they would lead to the production of two rings widely distinct from the equator. And, judging from what appears, we must hold that the laws of plutonic intrusion or upheaval, though more obscure than those of deposition, operate quite as independently of the earth's rotatory motion. Were the case otherwise, the mountain systems of the world, and all the great continents, would be clustered at the equator; and the great lands and great oceans of our planet, instead of running, as they do, in so remarkable a manner, from south to north, would range, like the belts of Jupiter, from east to west. There is no escape for us from the inevitable conclusion that our globe received its form as an oblate spheroid at a time when it existed throughout as a viscid mass. Nor is it unworthy of remark, that the same arrangement through which a fluid earth was moulded into this shape under the impulsion of the rotatory motion, also secured that when that earth came to be covered by a fluid sea, placed under the same impulsive influence, it should cling to it equably, like a well-fitted cloak, without falling off to the poles on the one hand, or accumulating in a belt round the equator at the other.

But time fails, and I cannot follow up this subject to its legitimate conclusions. Allow me, therefore, simply to state, that I must continue to hold, with Humboldt and with Hut-· ton, with Playfair and with Hall, that this solid earth was at one time, from the centre to the circumference, a mass of molten matter. Let us remember,—I employ here the words of Humboldt,-that the great chemist Sir Humphrey Davy, to whom we are indebted for the knowledge of the most combustible metallic substances, renounced his bold chemical hypothesis in his last work (Consolations of Travel) as 'inadequate and untenable;' and further, that, with the oblate sphericity of the earth and the planets to be accounted for, those who continue to hold what he rejected will be reduced, if they persist, to the unphilosophical