the earth's inertia, and to the upheaving of its continental ridges!

Before taking leave of this interesting part of the subject, it may be observed, that the whole tenor of the discourse puts an end to all fanciful or figurative conceptions which have been applied to the duration of the day, so frequently mentioned in this introductory part of Scripture.

The Dynamical System maintains, that it was a natural day of twenty-four hours, and requires, for its completion, the centrifugal impetus arising from the rotatory motion of 15° per hour, which the limitation of the above period, within natural bounds, can alone supply; and it besides requires that this force should have been put forth simultaneously with the introduction of the light, or, rather, that this should have been the cause of the upheaving of the continents and mountains, and the depression of the oceanic hollows, &c., as stated. For if the day were supposed to have been longer than twenty-four hours, there would be a deficiency of dynamical power to which to attribute the numerous inequalities of the earth's surface; while, on the other hand, if it be presumed that these geographical features have existed ever since the sphere was translated in space, besides the difficulty of accounting for their origin, there would be the dynamical power of rotation, at the rate of 15° per hour, too much, by having no adequate objects on which to show that it was expended. This treatise shows all those data to be at one, and perfectly reconciles them. By assuming the first diurnal rotation of the earth to have taken place, as in reality it did, on the first day of the Mosaic week, by considering the specified period" of evening and morning" to have been a natural day, measured by a revolution of the earth around its axis, and by attributing the change of form which it underwent, and the diversified appearance of its surface, to the force which this rapid diurnal movement, so instantaneously communicated, necessarily produced, we are relieved from all perplexity of mind, and made to see the whole to be parts of one grand and comprehensive plan: the work of creation carried on through innumerable ages, but completed in six natural days.

SECTION VIII.

CONCENTRATION OF THE LIGHT AROUND THE SUN; AND THE COMPLETION OF THE WORK OF CREATION.

CHAPTER XXXIX.

N the prosecution of the subject during the present chapter,

IN

I have to direct the attention to the fact that "the earth is, of itself, a non-luminous body, receiving its external light and heat from the sun;" and, then, to the following considerations which arise from it; namely, that there are only two ways in which the earth could, at this particular period, have been made to receive light and heat from another orb around which it circulates. Firstly, the simultaneous formation of the material body of the sun, with its luminiferous powers; and its being placed, thus doubly constituted, into the centre alike of attraction and of expansion; and then causing the earth to revolve in its orbital path around it. Or, secondly, by supposing that the material part of the sun to have been previously in existence, although not illuminated, the earth revolving around it by the same laws by which it now does; and that, while in this state, the light was made to concentrate around the previously dark nucleus as a luminiferous atmosphere, dispensing rays from every point of its equatorial circumference.

Against the first of these suppositions there are very many and insuperable objections. It is inconsistent, with what is known respecting the laws of matter, to conceive the existence of the earth, not only for three days, but for as many seconds, without presupposing the existence, likewise, of the other

planets, and the material body of the sun, as counterpoises to one another, in the mutual system of which the earth forms only one member. Again, it is impossible to imagine the existence of matter without attraction, or attraction in the solar system without revolution in appointed orbits through space; for without this last counterpoise to attraction the material universe would have gravitated into one vast and boundless whole-a universe of undivided matter! But if revolution in space be admitted, then there must needs have been a central mass round which, and the common centre of gravity, the revolution was to be performed by the revolving bodies; while, in addition to all other objections, there can be adduced the words of the record itself-"Let there be lights in the firmament of heaven:" for who, after having been made acquainted with the nature and constitution of the firmament, could, for a moment, suppose this to apply to the material bodies of the sun and moon, or imagine that it was ever meant that the firmament should be capable of upholding them, on the fourth day, in addition to those already in our system? Not so with respect to the latter of the two suppositions formerly mentioned; for then every conclusion is as consistently favourable to it as they are adverse to the former. According to the natural interpretation, or strict signification, of the Mosaic narrative, there was only this addition made to the laws which had been previously established-That there should be LIGHTS, a primary and a secondary light, introduced into the firmament of heaven; and which, by the mere act of being "set there,” were to become, to the earth, "signs, seasons, days, and years." In this no mention is made of causing the one sphere to revolve around the other; or of forming the solid materials of those luminaries which were to produce these effects; but it is strictly confined to the lights themselves, one of which was to be greater than the other, and they were to be "set in the firmament of heaven," which, from our knowledge of the earthly firmament, must be presumed to allude to the firmament of the sun.

Meditating upon this passage, under the consciousness of the earth having for ages revolved around the unilluminated solid nucleus of the sun, which assuredly was then the con

dition of our planet, its peculiar harmony will be recognised, not only with all the laws formerly instituted, but likewise with the original structure of the materials of the earth itself; while no difficulty will ever afterwards be experienced in fully comprehending this passage of Scripture, which, while it accounts for this wonderful operation, is remarkable for the characteristic and convincing simplicity of the words in which it is couched-language which, alone, could be employed by the Omnipotent, when He graciously informs us of the primary light being made to remain permanently in the centre of the system; and what a God-like labour it was, to cause that which, by its characteristic tendency, propends towards the circumference, to concentrate itself around the central orb of our system, and there to remain fixed and immovable to fulfil his future designs! Besides, it agrees most admirably with those views at present entertained, and considered to be the most scientific, as to the nature and constitution of the solar atmosphere. To verify this, while I may be allowed, for the unity of our argument, to disregard, as irrelevant to the inquiry, the merits of the contending theories respecting the intimate nature of light; a branch of natural phenomena, connected more directly with the luminiferous atmosphere which is supposed to surround the sun, will be followed up. The second part of the thirty-ninth Theorem states-" That a pencil of light, by the skilful application of certain refracting and absorbing media, can be polarized or separated into two distinct pencils; one whose pole is + 45°, and the other having its pole —45°.

This interesting announcement being essential to the future argument, some of the evidences on which it is founded will be given in continuation.

Sir David Brewster affords the following evidence, which is given so circumstantially, because it is inconsistent with perspicuity to abridge it :—

"If we allow a beam of common light to fall upon a rhomb of Iceland spar, and examine the two circular beams O E, formed by double refraction, we shall find

"That the beams O E have different properties on different sides, so that each of them differs, in this respect, from the beam of common light.

"These two beams, O E, are, therefore, said to be beams of polarized light, because they have sides or poles of different properties.

"Now, it is a curious fact, that if we cause the two polarized beams O E to be united into one, or if we produce them by a thin plate of Iceland spar, which is not capable of separating them, we obtain a beam which has exactly the same properties as a beam of common light.

"Hence we infer, that a beam of common light consists of two beams of polarized light, whose planes of polarization, or whose diameters of similar properties, are at right angles to to one another..

"It does not appear," he continues, "from the preceding experiments, that the polarization of the two pencils is the effect of any polarizing force resident in the Iceland spar, or of any change produced upon the light. The Iceland spar has merely separated the common light into its two elements, according to a different law, in the same manner as a prism separates all the seven colours of the spectrum from the compound white beam, by its power of refracting these elementary colours in different degrees. The reunion of the two oppositely polarized pencils produces common light, in the same manner as the re-union of the seven colours produces white light."

Sir John Herschel may be said to have summed up the evidence regarding these optical discoveries, when he favours us with the following account of their progress, which it has here been requisite to abridge :

"After a long torpor," he observes, "the knowledge of the properties of light began to make fresh progress about the end of the last century. The prosecution of the subject was encouraged by the offer of a prize on the part of the French Academy of Science; and it was in a memoir which received this honourable reward, in 1810, that M. Malus, a retired officer of engineers in the French army, announced the great discovery of the polarization of light, by ordinary reflection, at the surface of a transparent body.

...

"The new class of phenomena thus disclosed was immediately studied with diligence and success, . . . . and soon excited the highest interest that sort of interest which is raised when we feel we are on the eve of some extraordinary discovery.

The late Dr. Thomas

"This expectation was not disappointed. Young had been led to the idea that the same ought to hold good with light as with sound; and that, therefore, two rays of light setting off from the same origin at the same instant, and arriving at the same place by different routes, ought to strengthen, or wholly or partially destroy, each other's effects, according to the difference in length of the routes described by them.

That two lights should, in any circumstances, combine to pro

Optics, in Cab. Cyc., p. 157.