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water, and although not analyzed quantitatively, it left no doubt upon my mind as to its being protochlorid of iron; and the manner of its occurrence gave strong evidence of its being an original constituent, and not formed since the fall of the mass. Chloride of iron was apparent on various parts of the iron, by its deliquescence on the surface.

2. The meteoric iron from Campbell county, Tennessee.-This meteorite was discovered in July, 1853, in Campbell county, in Stinking creek, which flows down one of the narrow valleys of the Cumberland mountains, by a Mr. Arnold, and was presented to me by Professor Mitchell, of Knoxville. It is of an oval form, 24 inches long, 12 broad, and thick, with an irregular surface and several cavities perforating the mass. It was covered with a thin coat of oxyd; and on one-half of it chloride of iron was deliquescing from the surface, while on another portion there was a thin silicious coating. The iron was quite tough, highly crystalline, and exhibited small cavities on being broken, resembling very much in this respect, as well as in many other points, the Hommony creek iron; a polished surface when etched, exhibited distinct irregular Widmannstättian figures. The weight is 4 ounces. Specific gravity, 7.05. The lowness of the specific gravity is accounted for by its porous nature. The composition is as follows: Iron......

Nickel.....
Cobalt.....

Copper, too small to be estimated.

Carbon....

Phosphorus.

Silica..

97.54

0.25

0.6

1.50

0.12

1.05

100.52

=

Chlorine exists in some parts in minute proportion. The amount of nickel, it will be seen, is quite small, but its composition is, nevertheless, perfectly characteristic of its origin.

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3. The meteoric iron from Coahuila, Mexico (Fig. 2.)-This meteorite, now in the collection of the Smithsonian Institution, was brought to this country by Lieutenant Couch, of the United States army, he having obtained it at Saltillo. It was said to have come from the San

cha estate, some fifty or sixty miles from Santa Rosa, in the north of Coahuila; various accounts were given of the precise locality, but none seemed very satisfactory. When first seen by Lieutenant Couch, it was used as an anvil, and had been originally intended for the Society of Geography and Statistics in the city of Mexico. It is said, that where this mass was found there are many others of enormous size; but such stories, however, are to be received with many allowances. Mr. Weidner, of the mines of Freiberg, states, that near the southwestern edge of the Balson de Mapimi, on the route to the mines of Parral, there is a meteorite near the road of not less than a ton weight. Lieutenant Couch also states, that the intelligent, but almost unknown, Dr. Berlandier writes, in his journal of the Commission of Limits, that at the Hacienda of Venagas, there was (1827) a piece of iron that would make a cylinder one yard in length, with a diameter of ten inches. It was said to have been brought from the mountains near the Hacienda. It presented no crystalline structure, and was quite ductile.

The meteorite now before you (see Fig. 2) weighs 252 pounds, and from several flattened places I am led to suppose that pieces have been detached. The surface, although irregular in some places, is rather smooth, with only here and there thin coatings of rust, and, as might be expected, but very feeble evidence of chlorine, and that only on one or two spots. The specific gravity is 7.81. It is highly crystalline, quite malleable, and not difficult to cut with the saw. Its surface etched with nitric acid, presents the Widmannstättian figures, finely specked between the lines, resembling the representation we have of the etched surface of Hauptmannsdorf iron. Schreibersite is visible, but so inserted in the mass, that it cannot be readily detected by mechanical means. Hydrochloric acid leaves a residue of beautifully brilliant patches of this mineral.

Subjected to analysis, it was found to contain

[blocks in formation]

The iron is remarkably free from other constituents.

The specimen is especially interesting as the largest mass of meteoric iron in this country next to the Texas meteorite at Yale College. The three meteorites just described form an interesting addition to those already known, a very complete list of which has been lately

made by Mr. R. P. Greg, jr., to which I would refer all those specially interested in this subject. It is to be found in the Lond. Phil. Mag. for 1854.

A fact of much interest is that the number of meteorites already discovered in the United States is quite large, and, contrary to the general rule, the iron masses are the most numerous. The following table, by Mr. Greg, jr., shows at a glance the number of meteorites already found in different countries, the proportions of the stones and irons, and the average latitude of their localities.

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The number of these bodies which fall annually cannot be well determined. In the last sixty years the average falls observed are ten per annum; but of course the actual number must have far exceeded this, and some authors have supposed that not less than five hundred must fall annually on various parts of the surface of the globe.

In this lecture our object is not to enter into a detailed account of all the peculiarities of appearance of meteoric stones, either while falling or after their descent. The more immediate object is to consider the probable origin of these bodies; yet it is of general interest to mention some of those peculiarities before proceeding to the theoretical discussion.

Meteoric stones, as they fall, frequently exhibit light; are sometimes accompanied by a noise, and occasionally burst into several fragments. All of these phenomena are produced after they enter our atmo

sphere, which they do at a very great velocity; heat is developed in them by their friction against the air; the iron they contain is subject to combustion, which is augmented by the condensed condition of the atmosphere before the object while in rapid motion. All this suffices for the production of the light exhibited. Light does not always accompany the fall of these bodies--a fact which, it is reasonable to suppose, belongs especially to the masses of iron, which, from the compact nature of their structure, and their great conductibility, cannot become so readily heated on the surface as to reach the point of incandescence. The noise is produced by their rapid motion through the air, and their bursting by the combined effects of irregular expansion by heat, and certrifugal force produced by irregular resistance of the atmosphere; the latter being alone sufficient to bring about such a result, as is shown by the shooting of stone balls from a cannon. The velocity of these bodies will be discussed in another part of this lecture.

The lessons to be learned from meteorites, both stony and metallic, are probably not as much appreciated as they ought to be; we are usually satisfied with an analysis of them and surmises as to their origin, without due consideration of their physical and chemical characteristics.

The great end of science is to deduce general principles from particular facts. Thus terrestrial gravitation has been extended to the whole solar system, and, indeed, to the whole visible universe. The astronomer, however, has only proved the universality of this one law, and has found no evidence that any other force observed at the surface of the earth displays itself in any other sphere. However probable it may appear that the same laws affect terrestrial and celestial matter, it is none the less interesting to extend our proofs of this assumption, and meteorites, when looked upon in this light, acquire additional interest.

First. They lead us to the inference that the materials of the earth are exact representatives of those of our system, for up to the present time no element has been found in a meteorite that has not its counterpart on the earth; or if we are not warranted in making such a broad assumption, we certainly have the proof, as far as we may ever expect to get it, that some materials of other portions of the universe are identical with those of our earth.

Second. They show that the laws of crystallization in bodies foreign to the earth are the same as those affecting terrestrial matter, and in this connexion we may instance pyroxene, olivine and chrome iron, affording, in their chrystalline form, angles identical with those of terrestrial origin.

Third. The most interesting fact developed by meteorites is the universality of the laws of chemical affinity, or the truth, that the laws of chemical combination and atomic constitution are to be equally well seen in extra-terrestrial and terrestrial matter; so that were Dalton or Berzelius to seek for the atomic weights of iron, silica or magnesia, they might learn them as well from meteoric minerals as from those taken from the bowels of the earth. The

atomic constitution of meteoric anorthite, or of pyroxene, is the same as of that which exists in our own rocks.

An important peculiarity of the stony meteorites is, that their outer surface is covered with a coating strongly resembling pitch; this is a species of glass formed from the heated condition to which the meteorite arrives in its passage through the air, the heat acquired being sufficient to fuse the outer surface. The black color is due to the protoxide of iron combining with the silica. In most instances. the protoxide is formed from the oxydation of the particles of metallic iron in the mass.

Keeping in view then the physical and chemical characters of meteorites, I propose to offer some theoretical considerations which, to be fully appreciated, must be followed step by step. These views are not offered because they individually possess particular novelty; it is the manner in which they are combined to which especial attention is called. The first physical characteristic to be noted is their form. No masses of rock, however rudely detached from a quarry, or blasted from the side of a mountain, or ejected from the mouth of a volcano, would present more diversity of form than meteoric stones; they are rounded, cubical, oblong, jagged, and flattened. Now, the fact of form I conceive to be a most important point for consideration in regard to the origin of these bodies, as this alone is strong proof that the individual meteorites have not always been cosmical bodies; for had this been the case, their form must have been spherical or spheroidal. As this is not so, it is reasonable to suppose that at one time or another they must have constituted a part of some larger mass. But, as this subject will be taken up again, I pass to another pointnamely, the crystalline structure; more especially that of the iron, and the complete separation in nodules, in the interior of the iron, of sulphuret and phosphuret of the metals constituting the mass. When this is properly examined, it is seen that these bodies must have been in a plastic state for a great length of time, for nothing else could have determined such crystallization as we see in the iron, and allow such perfect separation of sulphur and phosphorus from the great bulk of the metal, combining only with a limited portion to form particular minerals. No other agent than fire can be conceived of by which this metal could be kept in the condition requisite for the separation. If these facts be admitted, the natural inference is that they could only have been thus heated while a part of some large body.

Another physical fact worthy of being noticed here, is the manner in which the metallic iron and stony parts are often interlaced and mixed, as in the Pallas and Atacama specimens, where nickeliferous iron and olivine in nearly equal portions (by bulk) are intimately mixed, so that when the olivine is detached, the iron resembles a very coarse sponge. This is an additional fact in proof of the great heat to which the meteorites must have been submitted; for, with our present knowledge of physical laws, there is no other way in which we can conceive that such a mixture could have been produced. Other physical points might be noticed; but as they would add nothing to the theoretical considerations, they will be passed over.

The mineralogical and chemical points to be noted in meteorites are

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