THE REVOLUTIONS OP 'THE GLOBE.
Tits French are certainly admirable cooks. With scraps, vege- tables, salt, and water, a Frenchman will turn you out a palatable soup, which shall be agreeable in combination, though its respec- tive ingredients were of no value by themselves. As the goodness of the materials increases, so will the quality of the dish ; though scarcely perhaps in proportion. The skill which disguised the vile, acts in a similar manner upon the excellent. The peculiar flavours are extracted, and combined in a capital dish; where, however, the native qualities of the original prcductions are changed and subdued, out of compliment to the character of the artist.
The national ability in the cuisine extends to compilation. However worthless the materials, a French litterateur generally contrives to throw something of animation and a sort of conven- tional grace into his productions, which show off to great advan- tage against the heavy hodgepodge of his English compeer. The quality of the workmanship does not perhaps rise with the value of the matter, but the utility of the work certainly increases, and so do the vivacious pains of the compiler. Still, in the closet as in the kitchen, the vanity of the Frenchman predominates : it is be, not his originals. He refers to them, for it is creditable to have mastered them; he praises them, fin- to praise is a mark of judgment, and eloquent eulogy is moreover praiseworthy in itself. But he aims at becoming the principal figure in his own piece, and rather gives the impression which the original authorities have made upon him, than a reflection of the ideas the perusal would convey to others. Hence, in exactness and fidelity, the higher class of English compilations probably exceed those of our neighbours; in spirit, animation, and that oneness of character which gives an air of originality to a work, they are inferior. Of French compilations of the bettermost kind, the Revolutions of the Globe, by Dr. BERTRAND, is one of the most agreeable we have met with.
The object of the author is to convey to the idlest and least learned reader an idea of the wonders of geology. To accomplish his intention in a manner which requires the easiest and admits with propriety of the most trifling mode of treatment, he addresses his nineteen Letters to a lady. The chief subjects lie discusses are—the general divisions of our globe; the probable origin, the workings, and the effects of volcanoes and earthquakes; the centre and crusts of the earth ; the different fossil remains both animal and vegetable, with some endeavours at clothing the dry bones of the antediluvian monsters, and a general view of the waters of the globe and of the surrounding atmosphere, both in their present conditions and conjecturally in their former states. 'His matter consists of the striking facts of geology, rather than of a view of the principles or a statement of the evidence on which they rest. His manner of discussion will best be shown by some specimens. The surface of the globe is not a new subject; yet see how in- teresting our author makes it— Our earth, as is well known, has the form of a spheroid, a little flattened to- wards the pules. Its radius is about 1500 leagues. The highest mountains do
not rise to more than two leagues above the level of the sea, and there are but few tracts naturally situated below that level ; and the greatest depths which have been reached by digging in the quarrieF, and more especially iu the mines,
do not exceed ISOO feet. The inequalities of the soil, then, are very trifling, when compared with the whole mass of the terrestrial spheroid; and if the depths of the pits dug from the surface strike U3 with awe—if the elevation of the mountains, whose summits we perceive to be lost in the clouds, confound us with astonishment, it is only because we judge of them by comparison with the extreme smallness of the objects which surround us. The earth, the superticies of which scents so unequal and rugged, would 'offer to the eye of an individual, capable of embracing the outline at a glance, only the smooth appearance of one of our artificial globes, at the iustaot when it comes from the ballets of the workman who has polished it. Let its suppose the terrestrial spheroid to be represented by a ball three inches in diameter. If we wished upon this ball to figure, in relief, the inequalities which are seen on the surface of the earth, the slightest protuberances, almost invisible to the eye, assisted by a microscope, would represent the highest moun- tains ; the slightest scratch which could be made on its surface would be deeper, in relation to its diameter, than are the greatest artificial cavities in proportion to that of the earth ; and the vapours which a single breath would cause to be condensed, would, perhaps, be too thick to represent the atmosphere, even to the height at which clouds are formed.
For us, imperceptible atoms, who vegetate in this slight stratum of humid air, there is no expression to describe our littleness and the weakness of our means, when we employ them to act upon the globe. Nevertheless, this puny atom has measured the earth, the dimensions of which crush him to nothing ; be has measured the sun, a million times greater than the earth ; he has calculated the distance which separates it from that orb whose brilliance his feeble gaze cannot sustaiu ; he has recognized in the myriads of stars which sparkle in the firmament, so many other suns spread through the immensity of the universe, around which revolve their respective systems of opaque globes, all of whose movements they regulate. Capable, in his diminutiveness, of raising his ideas to an expanse without bounds, the earth is no more to his enlarged conceptions than a grain of sand lost in the infinity of space.
Is there not in all this, 3Iaelatn, matter for much reflection on the superiority of the human mind, which enables it to comprehend objects of such magnitude, though nature seems to have condemned it to vegetate within so narrow a circle ? I will not, however, add another word on this topic. Let us only re- member, that in all which we shall have to observe upon the revolutions of the globe, our means of modifying it are so s.rall, that we can scarcely reckon for any thing the influence which nature has given us the power of exercising upon it. We commonly distinguish in the terrestrial spheroid two parts, the limits of which are, however, entirely arbitrary : first, the internal mass, that is to say, the central part, to which, without doubt, we can never internal secondly, the mineral crust which serves as an envelope to the Internal mass, and of which observation can make us acquainted with only the most superficial part. We may imagine this envelope to be from ten to twelve leagues thick. In the consideration of these two principal parts, we shall add, as subjects of separate study, first, the mass of waters, which covers more. than three- fourths of the superticies of the globe ; secondly, the atmospheric mass, a gase- ous matter which surrounds and embraces it in all its extent, and rises to an in- determinate height. We shall speak first of the internal mass. There is pro- bably no one who has not many times inquired whsther the earth continues to be pretty nearly the same throughout the whole extent of its depth, presenting to- wards its centre a series of strata analogous to those which are met with on the superficies ; or whether, at a certain depth, there is constantly found, at all points of the globe, one uniform substance filling up the whole of its interior. These questions, asked by every one, geologists have not failed to put to them- selves, and in order to answer them, hypotheses the most diverse have been framed. They have supposed the interior of the earth to be filled with water, or gas, or with enormous masses of loadstone, or with metals, either in a solid or liquid state. Diderot, in particular, in attempting to explain the magnetic action of the earth, regarded the internal part of the globe as formed of a vitri- fied nucleus upon which the external shell produces, by its friction, the same effect which the cushions of au electric machine produce upon its glass table or cylinder. None of these hypotheses can be sustained at the present day, as we know that they are incompatible with every thing that incontestible calculations may teach us respecting the constitution of our planet.
WHAT IS INSIDE THE EARTH?
We know, in fact, exactly the volume of the earth, and it is equally possible to calculate its weight. Natural philosophy and astronomy furnish us, in order to arrive at this knowledge, with two different means, both agreeing sufficiently between themselves. Roth give, as their result, a weight so considerable, that the interior of the globe must necessarily be five or six times more dense than the mineral crust, such as it presents itself to our observation in its tipper strata. It is, then, neither of gas, nor of water, that the internal mass is formed, nor even of the heaviest stories with which we are acquainted ; for even on this last supposition, the entire spheroid would still have a weight three or four times less than what the calculations assign to it ; it must, in fact, be com- posed of substances of a specific gravity equal- to that of the heaviest metals. These heavy substances, however, which are probably metallic, do not exist in the internal mass iu the state of solidity imparted to them by the temperature which prevails on the surface of the earth. Every thing tends to prove, that they are there subjected to the action of a heat capable of retaining them in a state of constant fusion ; and this supposition might, from the earliest periods of time, have been inferred from the enormous masses of liquid metallic sub- stances ejected from the bowels of the globe by the craters of the volcanoes,— substances which bear the most striking resemblance, in whatever place they are found, or however remote the time when they were projected to the surface of the earth. The mineral springs, and hot wells of every kind, some of which still retain the heat of boiling water on reaching the surface of the ground, offer a fresh proof of the temperature which prevails at a certain depth. These conjectures have been strengthened by experiments. Here is a hint for pushing them further— It will seem, perhaps, that to employ so many different modes to ascertain the degree of beat in the terrestrial strata situated beneath the soil, is to take very circuitous methods to arrive at that information which might be gained in a direct manner. Why not merely dig downwards till some obstacle prevents our further progress? Why not follow the counsel of Itlaupertuis, whom Voltaire so much rallied, as having suggested that a hole should be made as far as the centre of the earth? That would, assuredly, be the most certain means of knowing what can be discovered there, and it is only to be regretted that the enterprise is impracticable. To descend only to the depth of ten or twelve leagues would require an im- mensity of labour and expense. It worth!, neverthelesa, be an object of curiosity to attempt something of the kind, if carried only so far as to avail ourselves a the working. in the deepestmines in order to bore the ground from their level We might thus, at an expense not exceeding what a private individual might be able to appropriate to the experiment, sink a thesmorneter to the depth of MOO feet at least below these cavities. This depth week' give, on. Tech:a',
hypothesis. an elevation of 15 degrees above the heat of the deep mines; and we know that in some of these excavations the heat is already so great that the miners are obliged to work naked. But, if any government would undertake to assist in researches which would be en highly interesting to science, results much more conclusive might be obtained, and the question at least might be determined whether, at a distance comparatively very near thesurface of the ground—at some thousand toises, for example, below the deepest mines—the heat would nut become so intense as to prevent any further progress.
A CHOICE OE EVILS.
If the mineral crust were not so thick, the internal heat, becoming more sen- -sible at the surface of the groom), would cause a higher temperature than what -we experience in the present state of things ; bud, accordingly, every thing leads us to infer that the surface of the earth formerly had a much higher tem- perature than we now find it to possess. A great number of naturalists have even been induced to regard our globe as a small incrusted sun. According to them, its entire mass was at first incandescent, like that of the sun. In conse- quence of its movement through space, it was sufficietly cooled to permit the solidification of its most exterior envelope. This solid envelope must, upon this hypothesis, have increased in thickness ; and the earth, thus Cooling by slow degrees, is irrevocably doomed to become at last only a frozen mass, uninhabit- able by any human being, and revolving round a eon whose heat diminishing in a like gradual manlier will equally terminate in being entirely dissipated. No one has a right to despise such an opinion, for it was supported by Baron. But let it not too much alarm us, for other learned men have adduced very strong reasons to reassure us. One of the most celebrated among them (M. Fourier) has even proved mathematically, that in the existing state of things the internal heat of the globe, if indeed it has still any influence upon the temperature of its surface, cannot, at a medium, raise it more than the tenth of a degree whence it follows, that the whole amount of the cooling of the globe will not effect any appreciable change in the seasons of each climate, while the intensity of the heat supplied by the sun remains the same, and there is nothing to prove that the heat has diminished from the most distant periods. Several geologists, on the other hand, whose opinions, it is true, have no better foundation than that of Tinfoil's, present to us a prospect nut at all 1LOIC agreeable. They doom us, or rather our posterity, to behold the rivers, lakes, brooks, all the seas, and the ocean itself, dried up by gradual evaporation; until at length the parched earth shall be ignited by the sun. Of the two evils, I should prefer the latter ; it is more sudden, and the grand display of fireworks which it offers in perspective, alarms the imagination much less than that eternal icy death with which Ruffin menaced us. Let me add, that some chemists assure ter, that the earth will be renewed from its ashes, and that this grand combustion will produce a quantity of water so considerable, that it must continue evaporating for many centuries before any continents shall be again uncovered.
To the Letters, Dr. BERTRAND has prefixed an Introduction, containing some account of various theories of the earth which have been maintained by different philosophers. The Appendix consists of narratives of remarkable facts connected with volcanic eruptions and earthquakes, or of scientific points, the discussion of which might have encumbered the text. The translator has exe- cuted his task ably, and contributed some additional information in the shape of mutes.
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