gravitating matter which constitutes, ac- tion of the nebulous matter, which is therecording to Laplace and Humboldt, the Zo-fore conjectured to be dusty, not fluid. diacal Light; and to shooting stars and aero-The mass of comets is conjectured not to lites, celestial in their origin, terrestrial in exceed 1-5000th of the earth's at a maxitheir component parts, (iron, nickel, cobalt, mum, and perhaps not 1-100,000th at an managanese, chromium, copper, arsenic, average. tin, soda, potash, sulphur, phosphorus, and carbon,) which bring us down to the vulgar chemistry and geology of our own Earth. Of cometary astronomy we have (p. 105, &c.) an interesting synopsis which we should willingly have transferred to our pages were it not too long; besides, our readers will be more interested in parts of the subject more akin to Humboldt's own pursuits. It may be mentioned in passing, as a curious fact, that the earliest valuable observations, of comets are due to the Chinese, and extend as far back as the years A. D. 240, (under Gordian III.) 539, (under Justinian,) and 565. Our author does not fail to draw a contrast between the terror with which these bodies were then regarded throughout Europe, and the scientific composure of the Chinese. In 837, when a comet of alarming magnitude approached the earth, within twice the moon's distance, whilst Louis I. of France was trying to avert the impending danger by vowing to found a monastery, the countrymen of Confucius were coolly measuring the length of its tail and determining its course amongst the stars. The periods and eccentricities of comets have, as is well known, an enormous range. Three orbits are considered to lie wholly within the recognized limits of our solar system-1. Encke's comet, which revolves in 3 years, and whose aphelion or most distant point lies within Jupiter's orbit; 2. Biela's comet of 63 years extends its path beyond Jupiter's orbit, but far within Saturn's; 3. Faye's comet, (discovered in 1843, and of which the return has yet to be observed) is supposed to have a smaller eccentricity than any other known comet, and a period of 7 years, with an orbit lying wholly between those of Mars and Saturn. On the other hand the comet of 1680 is supposed to reach its aphelion at a distance of 80,000 millions of miles from the sun, forty-four times further than Uranus. Yet the nearest fixed star, whose distance has been approximately estimated (a Centauri,) is distant no less than 11,000 radii of Uranus's orbit, and the star 61 Cygni 31,000 radii. Yet this same comet of 1680 approached the sun's surface within 1-6th of the sun's diameter, or 7-10ths of the moon's distance from the earth. It was then moving with the velocity of about 250 English miles in a second, whilst at the other extremity of its eccentric orbit it must toil along at the rate of but 10 feet in a second, a speed comparable to that of many large rivers. Nor does it return to the sun until the lapse of 8800 years from the time of its departure. It is singular, that in enumerating (p. 118) instances of the near approach of comets to the body of the sun, our author has omitted that of 1843, of which the orbit was first calculated by an accomplished young astronomer, M. Plantamour, of Geneva, and shown to have a perihelion distance less than that of any previously known, even that of 1680. The comets of 1402, 1532, 1577, 1744, and 1843, were so bright that the nucleus was visible in broad daylight; but their well-defined disks are commonly excessively small, and indicate a diameter of but a few hundred miles, or even less. The cometary light is ascertained by Arago to be polarized, and therefore he concludes it to be reflected from the sun; whereas it seems to us that were the matter the same as that of the Sidereal Nebulæ, as has been supposed, it ought to be, like them, selfluminous. The tail is sometimes double, (1807, 1843,) and in 1744 was divided into six. The apparent length was, in 1618, 104°, or 14° greater than the distance from the horizon to the zenith. The comet of 1680 had an absolute extent of tail as great The next topic is one of general interest, as from the sun to the earth, (95,000,000 and is treated of with great fulness and miles.) A star of the 10th magnitude lost originality: the phenomena and origin of no sensible part of its brilliancy in being meteors, including aërolites and common eclipsed by Halley's comet in 1835 at a shooting stars. This part of the work (pp. distance of only 2/2 from the comet's 120-137) will be studied with interest by centre, (Struve,) nor do stars appear re- men of science as well as by popular readfracted out of their course by the interven-ers. It begins by recalling the general phenomena which are probably due to a common cause. The appearance of luminous fire-balls, sometimes so large and bright as to shed a visible gleam in broad daylight, is unequivocally connected by experience with the fall of aerolites or meteoric stones -as was the case (to cite only recent instances) in 1799 at Barbotan in the South of France; in 1794, at Siena in Italy; in 1804, at Weston in Connecticut; and in 1821, in the department of the Ardêche in France. Sometimes a small dark cloud appears to originate the meteoric shower, whose descent is accompanied by a noise like thunder. The fire-balls, which occasionally appear to exceed the diameter of the moon, have every intermediate magnitude down to that of common shooting stars-and this is the strongest, perhaps the sole evidence, for their identity of nature; both one and the other leave phosphoric trains behind them, a real phenomenon, and not due to an optical deception, as has been sometimes imagined (p. 394, note 30.) The important consideration which has recently recalled particular attention to these curious and beautiful appearances of luminous meteors, is their alleged periodicity. On this subject Humboldt says : New Continent from the Equator to the Herrn- It is impossible to deny the startling force of these recurring exhibitions, as leading naturally to the conjecture that meteors are Cosmical, and not atmospheric phenomena as Halley first supposed; for how, otherwise, can we account for a periodicity depending solely upon the time of 'Shooting stars fall either singly and rarely, year, that is, upon the earth's geocentric (sporadically) or in groups of many thousands. longitude or position in space? If the peIn the latter case they are periodical and gen-riodicity were certain, it would seem imerally move in parallel directions. Of periodic possible to entertain any other supposition groups the best known are the November-phe than that these bodies, the very same with nomenon (12th-14th of November,) and that of the Feast of St. Lawrence, (10th of August) whose "fiery tears" have long since been suspected by tradition, and in an old monkish Calendar,* to be a recurring meteorological phenomenon. Although a mixed shower of falling stars and fire-balls was seen in the night of the 12th-13th of November at Klöden, near Potsdam, and in 1832 throughout all Europe, from Portsmouth to Orenburg on the Ural river, and even in the Isle of France in the Southern Hemisphere, still the idea that great meteoric showers are connected with certain days was first occasioned by the observations of Olmsted and Palmer in North America, on the 12th-13th of November, 1833, when the falling stars appeared compressed like snow flakes about one spot in the sky, so that in nine hours not less than 240,000 must have fallen. Palmer, in New Haven, Massachusetts, recollected the meteors of 1799 (also on the 12th-13th of November,) which were first described by Ellicott and myself, and which it is proved by the observations which I have cited, were simultaneously seen in the Said to exist in Corpus Christi College, Cam bridge. the ferruginous (unoxidated) and stony masses (resembling dolerite, a trap-rock) which sometimes fall to the ground with such a velocity as to penetrate ten or fifteen feet into the soil (p. 122,) are independent planetary bodies circulating round the sun (not the earth) with a mean velocity, distance, and period similar to that of the earth in its orbit; for under no other circumstances could they remain thus, as it were, suspended in space, ready to meet the earth at the points of mutual intersection of their respective orbits (the orbit of the meteors being more or less inclined to that of our planet.) Undoubtedly no more exciting question in natural philosophy could be started: we will briefly add such particulars from the details given by Humboldt as may assist in forming a fair judgment, though probably the cautious reader may be of opinion that the time for decision has not yet arrived. The most important observations, next 'A striking confirmation of the opinion of to the periodicity, concern the absolute the Cosmical origin of such phenomena was height, velocity, and magnitude of these obtained by Denison Olmsted of New Haven bodies, including, for the present, fireballs (Massachusetts,) who has shown that, from the testimony of all observers, the fireballs and falling stars in one category. From the and falling stars of the 12th and 13th of Noobservations of Brandes and Benzenberg, vember, 1833, appeared to be directed from the height varies from 16 to 140 English one and the same point in space near Leogeographical miles. If this estimate be cor- nis; nor did they deviate from that origin, alrect, some shooting stars are undoubtedly though the star changed its apparent altitude seen within the limits of the atmosphere, and azimuth during the long continuance of the observation. Such an independence of but others are as certainly far beyond the the earth's rotation proves that the luminous extreme bounds which have ever been as- bodies reached our atmosphere from the planetsigned to it. Hence the atmosphere can- ary spaces beyond it. From Encke's calcunot be necessary to their luminosity, and lation of the whole observations made in the indeed it is not easy to conceive how it United States between the latitudes of 35° should be so, in the state of extreme tenu- and 42°, they must have come from the point in space towards which the earth's motion ity which its upper regions must present. was then directed.'-Kosmos, p. 126. The apparent or relative velocity of the meteors (supposing the earth at rest) would be by the same authorities from eighteen to thirty-six nautical miles a second, which can only be compared to planetary velocities. In this our author finds a powerful argument against those who have ascribed the origin of these bodies to lunar volcanoes. For the velocity with which a body launched from the moon with just sufficient speed to escape from the lunar attraction (8000 English feet) would reach the earth, would be no more than six miles a second. The remaining velocity of twelve to thirty miles a second would therefore be due to the projectile force of the lunar volcano, which far exceeds all probability. It has been supposed that the less exact observations in August confirm the same view. But it is worthy of note that such an hypothesis as to the general direction of the meteors, must not only be universal if true, but supposes the meteors to be directed in their orbits diametrically opposite to the earth's motion at the moment; for, as we have already observed, it is mechanically impossible that they should be still in space, and the earth merely dash through them; and in any other case than a concurrent or diametrically opposed motion to the earth's, their apparent paths must be the resultant of their own motion and that of the earth, and therefore not directed from the point towards which the earth is moving at the time. These considerations suggest doubts upon which our limits do not allow us to enter. The height of the meteors and their apparent size being known, their real dimensions may be calculated; and the largest, according to Humboldt, vary from 500 to 2600 (French) feet in diameter. These It is impossible, however, to deny that are vast indeed, worthy of being consid- the considerations which we have detailed, ered planetary fragments. The meteor of seem to confirm the opinion entertained even the 18th August, 1783, observed in Eng- by some Grecian philosophers, that aerolites, land, was apparently as large as the moon, at least, are uncombined portions of the and was computed to have exploded at a matter of which our planetary system is height of fifty miles, whilst moving with a composed. The fact that their constituvelocity of at least twenty miles a second, ents (already enumerated) include (so far and to have had a diameter of half a mile :* as our chemical analyses extends) no inyet the fragments were never found. The gredient not already recognized as composlargest known meteoric masses (two in ing the crust of our planet, is highly interestSouth America) have, according to Huming and perhaps unexpected. But instead boldt (Kosmcs, p. 123,) a length of be- of drawing the conclusion that therefore tween seven and eight feet; but they are they must be of terrestrial origin, we agree doubtless only fragments. with Humboldt, that it is more philosophiAnother circumstance of much import-cal to imagine (as Newton is said to have ance is the general direction of apparent motion of these so-called periodic streams. On this point we shall give Humbolt's own done) that the matter of all the bodies of our system is nearly alike; nor will it take away from the interest with which the geologist regards the meteoric fragment which he has been fortunate enough to secure for his cabinet, that it represents a portion of the rough material of the universe, that which Omnipotence has elsewhere wrought into suns, and planets, and satellites; it is a portion of primæval chaos. rections, attested by almost every author until the supposed discovery of their radiation from the constellation Leo; the fact that more than thirty years elapsed in our own day, during which they are only once recorded to have been seen; the fact that whilst hundreds of thousands of meteors have been seen in one night at one place, no single meteoric mass has fallen synchronously at any known point of the earth's surface, but that, on the contrary, aërolites have fallen indifferently at every season of the year; the fact that these meteoric showers are sometimes so local, that in 1837 they made a great show in England, but constituted no phenomenon at all in Prussia, where they were carefully watched for ;—all these circumstances constitute unexplained difficulties. How to reconcile them with any theory-nous ignorons comme on l'ignorait du temps d'Anaxagore.' The doctrine of the periodicity of the meteors, of their fixed direction in space, and their consequently forming a zone of revolving atoms in space, was quickly seized upon by the astronomers and naturalists of Germany, and was carried out perhaps beyond the limits of a rigorous induction. Not only was the periodicity in our own day admitted (the far more numerous blank years than those distinguished by the meteors being overlooked,) but old chronicles were ransacked for records of similar appearances. Considering that such occur rences were almost as carefully registered in the annals of superstition as in those of science, it is not wonderful that in the course of nine centuries three or four such From the digression on meteors our audisplays should be authentically noticed as thor returns to sidereal astronomy, in which occurring about the same time of year he gives a neat summary of what is known (Kosmos, p. 398.) Even, to obtain this or inferred respecting the physical condipartial confirmation, a latitude of almost a tions and distances of the fixed stars, the month required to be allowed. But this proper motion of our own system (p. 149,) circumstance no way disconcerted the Ger- and of double stars about their common man astronomers: they forthwith imagined centres of gravity (p. 152.) The luminous a precession of the nodes of the meteoric phenomena of occasional and variable stars ring with the earth's orbit, which causes a he elegantly and justly describes (p. 160) continual retardation in the period of con- as Voices of the Past '-(Stimmen der junction. But more than this, a German Vergangenheit.) These topics are pretty writer of credit has attempted to explain an well known to English readers, particularly anomalous meteorological fact (which, from Sir John Herschel's excellent writhowever, very probably depends upon the ings. local position of Europe,) the occurrence, namely, of some days in February and May, which are colder than the regularity of the annual curve of temperature would assign, to the intervention of this problematical zone of asteroids between the earth and sun at these periods! We are surprised to see that our author lends his distinguished countenance to this most rash and improbable hypothesis. Whilst the cosmical origin of true aerolites may be admitted to be more than barely probable, long and patient experience must be required before the November phenomenon' can be placed in the same category. The common nature of true meteorolites and falling stars, though once admitted by the sagacious Chladni, was finally rejected by him, and was also rejected by Humboldt himself long after he had observed the November meteors of 1799* The great diversity in their di Humbolt, Relation Historique, 8vo., iv. 47. At last we descend upon terra firma, and our author proceeds to a description of our globe and its phenomena. He gives first an interesting detail of the physical bounds of our acquaintance with it-limited_indeed, compared to its vast extent. The greatest depth below the sea-level to which the solid earth has been penetrated is about 2000 feet, or little more than 1-10,000th of the earth's radius; but the unfathomed ocean has been penetrated by Sir James Ross's lead to a depth of 25,400 feet, or nearly five miles, no bottom being found. The depth of the trough-shaped geological basins of the coal formations (containing fossils) in Belgium, is, from probable data, estimated at 5000 or 6000 feet below the surface of the sea. The highest of the Himalaya (Dhawalagiri) rises to 28,000 English feet, though that height has never been attained by man. When to this we Ibid., p 52. add that volcanoes pour forth matter deriv- | still more fantastical dreams. The internal ed (according to Humboldt, p. 166) from a depth of 25 English miles or more, we have an idea of the smallness of the por tion of our earth (a spheroid nearly 8000 miles in diameter) which we can explore. The lowest exposed part of the terrestrial surface is the Dead Sea, which is (Kosmos, p. 419) 1300 feet below the Mediterra nean. sphere is by and bye peopled with plants and animals,* upon which two little subterranean lustre. An equable temperature prevails in planets, Pluto and Proserpine, shed their mild these terrestrial spaces, and the air, rendered luminous by compression, might well allow us to dispense with the internal planets. Near the North Pole, in lat. 82°, is a huge opening, whence the Polar lights stream forth, and by which we can enter the interior of our globe. repeatedly and publicly invited by Captain Sir Humphry Davy and myself have been Symmes to such a subterranean expedition !— Kosmos, p. 178. Astronomy, geodesy, and modern physics, enable us, however, to determine not only the size and figure of our globe, but its solid contents, compared to a given bulk, for instance, of water. The size and figure. The only reasonable notion which we are more or less completely determined by can form of the interior condition of our three methods;-from the lunar inequali- planet is derived from the observed inties, by the measurement of degrees, crease of temperature as we descend in and by pendulum experiments: on the two mines or examine water rising to the surlast methods our author has collected in face from Artesian bores. Baron Humthe notes (pp. 421-424) some curious and boldt gives (note 8 p. 426) a number of the valuable information. The still more in- individual results which lead to the general teresting question of the earth's mass and conclusion that the rate of increase is density (Kosmos, p. 176, and p. 424) is about 1° Cent. for 92 French feet of desolved also by three methods;-by the at- scent (1° Fahr. for 54 1-2 English feet. traction of the plumb-line by mountains, It is plain that if this rate be uniform, or -by the irregularities of the pendulum, tolerably uniform, all known substances and most satisfactorily and elegantly by would be in a state of permanent fusion at the balance of torsion of Mitchell and no very great depth. Humboldt estimates Cavendish. In treating of the last, our the depth at which granite must be fluid at author has most unaccountably omitted the 21 English miles (Kosmos, p. 181,) which capital experiments of Mr. Baily, which is less than five times the height of the have reduced the previous ones to mere Himalaya, and little more than 1-400th of matters of history, and which were already well known at the time at which Kosmos appears (by internal evidence) to have been written.t The state of the earth's interior remains an open question;' and as the mention of it is the only part of Kosmos which can by possibility provoke a smile, we give our readers the benefit of it. the earth's diameter. In treating of the In connexion with the general question of the earth's heat our author treats of Magnetic phenomena, as being probably caused by electricity, and through electrici'In order to bring the known small ellipticity ty by heat. Speaking of the almost simulof the earth into conformity with the supposi-taneous disturbances of the needle over tion of the uniform indefinite compressibility of its substance, the ingenious Leslie has de-large spaces of the earth's surface, he scribed the earth as a hollow shell, filled with says:the so-called imponderable substances possessed of prodigious repulsive power. These hazarded and arbitrary opinions called forth These synchronous perturbations may serve for the determination of geographical longitudes within certain limits, like Jupiter's satellites, signals, and well-observed falling stars. We learn with astonishment that the movements of two small magnets, even were they suspended deep in the interior of the earth, may serve to measure the distance be Halley seriously entertained such an idea, and compares the earth to an habitation of several stories, inhabited within and without. - Phil. Trans., 1693, quoted in Kosmos, p. 425. |