port upon the State of Astral Observation, made to Count Ouvaroff, Min. of Publ. Instr. and Presid. of the Imperial Acad. of Sciences, by Prof. F. G. W. Struve; May 19, 1847. Petersburgh.

Table of the Time required by the different Magnitudes of Stars, for the passage of their respective Emissions of Light to our Sup. The Earth may be safely taken to be the same, as the difference is only a very minute fraction.

"And these are SUNS! Vast, central, living fires,
Lords of dependent systems, kings of worlds
That wait as satellites upon their power
And flourish in their smile. Awake, my soul,

And meditate the wonder. Countless suns

Blaze round thee, leading forth their countless worlds!
Worlds, in whose bosoms living things rejoice,

And drink the bliss of being from the fount
Of all-pervading love. What mind can know,
What tongue can utter, all their multitudes?
Thus numberless in numberless abodes!

Known but to THEE, Blest Father! Thine they are,
Thy children and thy care; and none o'erlooked
Of thee. No, not the humblest soul that dwells
Upon the humblest globe that wheels its course
Amid the giant glories of the sky;

Like the mean mote that dances in the beam
Amongst the thousand mirror'd lamps, which fling
Their wasteful splendour from the palace-wall.
None can escape the kindness of thy care;
All compass'd underneath thy spacious wing;

Each fed and guided by THY powerful hand."

Prof. Henry Ware, jun., Cambridge Univ. Massachusetts. For the citation I am indebted to Dr. W. B. Carpenter's Popular Cyclop. vol. iv. 1843.

[B b.]

Referred to at page 32.

ON THE THICKNESS OF THE SOLID CRUST OF THE EARTH.

"As for the internal heat of the earth, I am of opinion that it ought not to be considered as an hypothesis, but as a fact well grounded on numerous phenomena." Prof. Gustav Bischoff, of Bonn, in Jameson's Journal, Jan. 1841, p. 14.

"All the calculations,-if they can be at all trusted, tend to prove that the earth's crust is not much more, and perhaps less, then twenty miles in thickness: and if this be so, the crust may indeed be well compared with a thin sheet of ice over a frozen pool.”—Mr. Darwin, in Memoir on the Connexion of certain Volcanic Phenomena in South America, Geol. Trans. second ser. vol. v. p. 608, 1840. This able philosopher uses the language of deferential caution from respect to Mr. Parrot, (known for his observations on the Caspian Sea, &c.) but with little or no doubt in his own richly-informed mind. In this interesting Memoir, Mr. Darwin brings much evidence to establish the position, that the crust of the earth rests upon a mass of melted mineral matter, whose undulations, with other modifying causes, produce elevations, earthquakes, and volcanos. He has eminently the talent of simple but graphic description, and luminous deduction. Considering the extent of the field of action, a space, in the instance considered, of little less than 7000 miles,-"and likewise the symmetry of the whole, we shall be deeply impressed with the grandeur of the one motive power which, causing the elevation of the continent, has produced, as secondary effects, mountain-chains and volcanos. The same reasons, which led me to the conviction that the train of connected volcanos in Chile and the recently uplifted coast, together more than 800 geographical miles in extent, rested on a sheet of fluid matter, are applicable, with nearly equal force, to the areas. beneath the other trains." After enumerating several considerations, he continues: "It appears to me that there is little hazard in assuming, that this large portion of the earth's crust floats in a like manner on a sea of molten rock. Moreover, when we think of the increasing temperature of the strata, as we penetrate downwards in all parts of the world, and of the certainty that every portion of the surface rests on rocks which have once been liquefied;—when we consider the multitude of points from which fluid rock is annually emitted, and

the still greater number of points from which it has been emitted during the few last geological periods inclusive, which, as far as regards the cooling of the rock in the lowest abysses, may probably be considered as one, from the extreme slowness with which heat can escape from such depths;—when we reflect how many and wide areas in all parts of the world are certainly known some to have been rising and others sinking, during the recent æra even to the present day, and do not forget the intimate connexion which has been shown to exist between these movements and the propulsion of liquefied rock to the surface in the volcano ;- we are urged to

include the entire globe in the foregoing hypothesis.-The furthest generalization, which the consideration of the volcanic phenomena appears to lead to, is that the configuration of the fluid surface of the earth's nucleus is subject to some change,--its cause completely unknown,- its action slow and intermittent, but irresistible." Pp.

629-631.

But justice to this subject requires it to be stated that Mr. William Hopkins has applied his pre-eminent talents in mathematical analysis to the solution of this problem. Of this laborious investigation he has given the processes and the results, in four papers, communicated to the Royal Society in the years 1838, 1839, and 1842, "On the State of the Interior of the Earth ;" and published in the Philos. Trans. of those years. That the entire mass of the earth was originally in a fluid state, and that, by cooling, it has obtained a superficial coating of solidified matter, was first adopted as a result of astronomical considerations, but is now corroborated by the discoveries of geology. It occurred to Mr. H. that an indirect, but sure test of the truth of the hypothesis might be derived from the consideration of the Nutation of the Earth's Axis, a fact arising from the attractions of the sun and the moon, which produce the Precession of the Equinoxes. It is obvious that this nutation must affect the earth differently on the supposition of its being a fluid contained in a solid spheroidal shell, from what it would do if the globe were throughout a solid mass. Equally is it to be expected that differences of result will be produced according as the quantity of the contained fluid is less or greater; that is, as the thickness of the containing crust is greater or less. An indefinite number of conditions is thus presented for selection and investigation. To the immense labour of these operations, Mr. Hopkins applied himself, with his characteristic power and perseverance. Now the amount of the gyratory change constantly produced by the nutation of the pole is astronomically known. But the amount, as deduced from

the hypothesis of the earth's being composed of a heterogeneous solid shell inclosing a heterogeneous fluid, will not agree with the actually known amount, unless the ellipticity of the interior surface of the shell were less by a certain quantity than that of the outward surface. Finally, Mr. H. arrives at the conclusion that the thickness of the crust, to answer all the conditions, must be at least equal to one-fourth or one-fifth of the distance from the outer circumference to the centre of the earth; in other words, that the thickness of the solid envelope of the globe cannot be less than 800 or 1000 miles.

Here then is an astounding difference from the conclusion before mentioned, that in which so many eminent and accomplished physicists agree, and of which the evidence appears unexceptionable. But Mr. H. has furnished a mode of conciliation. He supposes that the solidity of the crust is not everywhere the same, but that there are insulated fluid masses, or what may be called vesicles, interspersed through it, containing portions of more fusible matter, and which is actually in a state of fusion, forming subterranean reservoirs or lakes, some of which are distinct, and others communicating by passages of different degrees of openness or obstruction. This he proposes for the explanation of the phenomena of volcanos. We must extend the idea, by supposing an extensive distribution of those fiery lakes, so as to cause the observed ratio of the increase of temperature in the descent of mines.

This investigation has produced another very important result, in demonstrating that no change has taken place in the direction of the earth's axis, from the epoch of the formation of the external crust.

Fourth ed. On this subject, at the sitting of the Paris Academy of Sciences, Dec. 9, 1844, "M. Elie de Beaumont made some observations on a question submitted for consideration, viz. What relation exists between the progressive cooling of the earth and that of its surface? M. de B. thinks that the experiments made by M. Arago, in the gardens of the Observatory at Paris, with thermometers sunk in the earth at various depths, furnish the most essential elements which are necessary for the solution of the problem. According to this solution, the antiquity of the period, when our globe was entirely incandescent, is of a remoteness which defies calculation." Athenæum, Dec. 28, 1844; p. 1202.

[C.]

Referred to at page 41.

ON THE NUMBER OF SPECIES IN THE EARLIER FOSSILIFEROUS ROCKS.

THIS proposition, as it stood in the first edition, expressed the doctrine, which till lately was received among geologists, that the organic remains found in the earliest rocks possessing any such remains at all, are "the fewest" in proportionate numbers. But the recent herculean toils of Mr. Murchison have opened new fields of view upon this interesting subject. The proposition is a little altered, that it may be in accordance with the observation of that distinguished geologist; "Another remarkable fact illustrating this point of inquiry is, that although the older fossiliferous strata often contain vast quantities of organic remains, the number of species is much smaller than in more recent deposits." Silur. Syst. p. 583.

It is interesting to observe the careful and cautious progress of Geology, as in other respects, so in this. Seven years before the publication of Mr. Murchison's work, Sir Henry De la Beche had treated this subject with his characteristic judgment and sagacity. I will cite a few paragraphs, as specimens of the penetration and anticipations of his geological mind, while the facts of the case were not as yet brought clearly to light; and with a wish also to excite my readers to peruse the whole passage. It must be premised that the German term grauwacke, now generally disused, must be understood as the same with, or including, the Silurian System.

"Although, when we regard the mass of the grauwacke rocks, we are struck with the minute proportion that organic remains bear to the whole, we must still perceive that the atmosphere was capable of supporting vegetation; and the seas of sustaining zoophytes, crinoidea, annulata, conchifera, mollusca, crustacea, and fish. What other creatures existed, we are unable, from the absence of their remains, to judge: it may however be by no means unphilosophical to conclude that vegetation did not exist alone on dry land, but that, consistently with the general harmony of nature, it afforded food to terrestrial creatures suited to the circumstances under which they were placed.” [Yet no vestiges of such creatures have been found.]"Whatever the kind of animal life may have been which first appeared on the surface of our planet, we may be certain that it was consistent with the wisdom and design which has always prevailed throughout nature; and that each creature was peculiarly adapted to that situation designed to be occupied by it." Geological Manual; third ed. pp. 428, 429; 1833.