Recapitulation.-1. All observations agree in demonstrating that the aurora borealis is a phenomenon taking place in our atmosphere, and that it consists in the production of a luminous ring whose center is the magnetic pole, and having a diameter more or less large.

2. Experiment demonstrates that in causing in highly rarified air the reunion of the two electricities near the pole of an artificial magnet, a small ring of light is produced similar to that which constitutes the aurora, and having a like movement of rotation.

3. The aurora is consequently due to electric discharges taking place in the upper regions between the positive electricity of the atmosphere and the negative electricity of the earth-the electricities being separated by the direct or indirect action of the sun, principally in the equatorial regions.

4. As these electric discharges take place constantly, though with varying intensity, depending on the state of the atmosphere, the aurora should be a daily phenomenon, more or less intense, and consequently visible at greater or less distances, and only when the night is clear-which accords precisely with observation.

5. The phenomena that attend the aurora, such as the presence and form of the cirro-stratus clouds, and especially the disturbances of the magnetic needle, are of a kind to demonstrate the truth of the electric origin attributed by the author to the aurora-an hypothesis with which these phenomena correspond even in their minutest details.

6. The aurora australis, according to the few observations on it which have been made, presents exactly the same phenomena as the aurora borealis, and is explained in the same manner.

ART. XXXVIII.-Notice of three ponderous masses of Meteoric Iron at Tuczon, Sonora; by CHARLES UPHAM SHEPARD, M.D.

THE first intimation concerning the locality here noticed, was afforded in 1851, at the Meeting of the American Association for the Advancement of Science, on the occasion of my describing before the Chemical and Natural History section of that body, the meteoric stone of Deal, New Jersey. Dr. J. L. Le Conte being present, and having just returned from California through the province of Sonora, stated to the meeting, that "while passing through the village of Tuczon, a frontier town of Sonora, near the Gila, in the month of February previous, he observed two large pieces of meteoric iron, which were used by the blacksmiths of the town for the purposes of anvils. He was unable to procure any specimens from these bodies; but was guided to a cañon

Second Series, Vol. XVIII, No. 54.-Nov., 1854.

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between two mountain ridges in the immediate vicinity from which both pieces had been taken, where the masses of meteorites were so abundant as to have given name to the cañon. He had not before heard any account of this remarkable circumstance, and had considered it an interesting subject for observation."*

Nothing farther was brought to light respecting this very remarkable locality, until the present season, on the return of Lieut. John G. Parke, of the United States Topographical Engineers, from his scientific explorations in Sonora, when he had the goodness to address me a letter of inquiry respecting them, attended with about an ounce weight for my examination, which he had procured in person from one of the masses.

Lieut. Parke observed in his letter that "the Alcaide and Commandante would not consent to our removing the masses, even had we possessed the means; but by dint of two hours hard labor, we managed to chip off a few fragments, which I hope may serve the purposes of analysis."

I immediately set myself to the best examination of the subject, which the limited supply of materials and the facilities at hand, permitted.

The fragments were small; the largest piece not weighing above one-quarter of an ounce, and that somewhat battered by the process employed for its separation. Still, it showed the natural outside of the meteor. It was destitute of a well marked crust, and much coated with oxyd of iron, evincing in common with the other fragments, that this iron is prone to undergo a rapid oxydation on exposure to the weather.

The fresh surfaces presented the color and lustre of white castiron; though it is not brittle, or granular in its fracture. A close examination of a fresh surface, produced by the cold chisel, reveals frequent white spots, of the size of a pin's head and smaller, scattered in every direction, and without any very perceptible order. These spots seem to be owing to the presence of an earthy powder, which adheres closely to the iron, and indeed seems partially imbedded therein. When such a surface is highly polished on the burnishing wheel, the spots disappear; but are renewed again on the application of acids, in the etching process. They then come into view, rather more circumscribed in their areas than before; but of a very determinate figure, being mostly rounded or oval, sometimes with angular indentations in their borders. They are never rhomboidal or rectangular in their outline, after the manner of the much larger earthy grains, or crystals, in the Atacama iron, which render the latter porphyritic, when cut into slabs. The Tuczon iron on the contrary, when thus polished and etched, is amygdaloidal only; and to discern this character thoroughly, requires the aid of a microscope.

Proceedings of the American Association for the Advancement of Science, Sixth Meeting, p. 188.

The acids act very tardily on the iron, and require to be aided by heat, before the action will fairly commence. No decided crystalline structure is developed in the process; though the fragments experimented on, being small, and considerably altered in molecular texture by the force applied in their separation from the parent mass, it would not be safe from this trial perhaps, to conclude against a crystalline structure in the main portion of the iron. Sp. gr. 6.66, which corresponds very nearly with that of the Atacama iron, as determined by Turner, whose trial specimen no doubt included the earthy constituent of that iron.

=

No sulphur was detected in those fragments that were acted upon by acids; but here again, it would not be strange if this very common element of meteorites should hereafter be detected, when a larger portion of the mass comes to be examined.

The most striking phenomenon that presented itself during my examination of the Tuczon iron, was the following. A white, insoluble powder came into view throughout the liquid, as the solution of the iron proceeded in nitro-hydrochloric acid; and at the conclusion of the process a considerable precipitate of this powder was obtained, among which were little ovoidal grains of a milk-white mineral and occasionally also, others of the same figure that were perfectly limpid, like hyalite; while others still were milky on one side and limpid on the other, thus evincing that the milky and the limpid mineral, was one and the same species. Indeed I was led to regard the mealy powder also, as partaking of the same nature; and such was the general resemblance of the whole, to the mineral I have called chladnite, in the meteoric stone of Bishopsville, South Carolina, that I am led to refer this earthy substance to that species: an opinion which is the more probably correct, as I found the acid solution to contain decided traces of magnesia, an earth which it is most likely proceeded from the partial decomposition of portions of the pulverulent, earthy ingredient of the meteoric iron, and not from the iron-alloy. Should this view of the unknown substance prove correct, it will be the first instance in which it has been found in an iron-mass. We shall then have (astro petrologically considered) a second species of meteoric iron, with an earthy admixture; the first being the previously known peridotic iron, and the second, that here pointed out, viz., the chladnitic iron.

The nitro-hydrochloric solution of the iron, afforded with ammonia in excess, a deep blue liquid, indicative of nickel in a very decided proportion, to the iron.

It remains only to state a few additional particulars concerning these iron-masses, derived from a later letter of Lieut. Parke, which he kindly permits me to annex to this notice.

"The three masses were found in a cañada of the Santa Rita Mountain, about 25 or 30 miles to the south of Tuczon. Two of them were shown to us by the Commandante; both being

used as anvils. One lies within the Presidio, and is of a very peculiar form, it being annular, and somewhat like a seal-ring of huge proportions. Its exterior diameter is about three and a half feet; its interior about two. It weighs nearly 1200 lbs. The other piece is in front of the Alcalde's house. It weighs about 1000 pounds, and has an elongated prismatic form, serving well the purposes of an anvil. It is partially buried in the soil, but having two feet of its length projecting above the ground. The third piece I did not see; but was told that it was much smaller than either of the others. By permission of the authorities, our blacksmith undertook to cut off some specimens, in which, however, he almost entirely failed-the metal being so tough and hard. It yields to the hammer, and has a clear ring, not unlike that of bell-metal. The surfaces were rounded, and rusted,-closely resembling a mass of refined cast-iron that had been exposed to the action of the weather for a long period. The surfaces that have received the blows of the hammer, where used as an anvil, are quite polished.

"To obtain these specimens would be attended with no little difficulty, owing to the remoteness of the locality, and the brokendown condition of animals when reaching this point."

The route of transportation recommended by Lieut. Parke, is that, via. Fort Yuma, distant 275 miles from the locality, on the California side; and from thence by water, to the head of the Gulf of California. Measures are already on foot for the removal of one or more of the masses, to this part of the country, which it is greatly to be desired will be crowned with success.*

ART. XXXIX.-Reëxamination of American Minerals: PART IV-Boltonite; Iodid of Silver; Copiapite; Owenite; Xenotime; Lanthanite; Manganese Alum; Apophyllite; Schreibersite; Protosulphuret of Iron; Cuban; by J. LAWRENCE SMITH, M.D., Prof. Chem. Med. Depart. University of Louisville.†

37. Boltonite, identical with Chrysolite.

BOLTONITE was first described as a new species by Professor C. U. Shepard. He made the specific gravity from 2.8 to 2.9. It was subsequently examined by Professor Silliman, Jr., who found

*The above Sonora meteoric irons were described and illustrated with figures in a paper by Dr. J. Lawrence Smith, presented to the American Association at its meeting at Washington in April last a paper which was to have appeared in our last number, but is still delayed. The masses were seen by officers of the late Boundary Commission, and figures are published in Bartlett's Personal Narrative (8vo, 1854), ii, 298.-EDS.

The absence of Mr. G. J. Brush from America, who was associated with me in the first three parts of these reexaminations, makes it necessary for me to continue them alone and the absence of his valuable assistance is a matter to be regretted by all who take any interest in the subject.-J. L. 8.

3.008 as its specific gravity, with a hardness of from 5 to 6: his analysis gave for its constituents:*

With this knowledge of the mineral, I undertook its examination, on specimens in the gangue furnished me by Prof. Shepard. Examination of different portions separated mechanically from the gangue, made it very evident that the mineral was more or less mixed with other substances which had escaped observation, for no two analyses agreed; and it was soon discovered that it was impossible (from the specimens in my possession at least) to separate Boltonite in a state of purity without the aid of other means than had been adopted.

Boltonite, as is well known, occurs at Bolton, Mass., disseminated in irregular masses and grains in a white limestone. If a piece of the mineral in its gangue be placed in cold dilute hydrochloric acid, the limestone is readily dissolved, and a mass left, which is seen to consist of asbestus, dolomite, a little mica, small crystals of magnetic iron, and a greenish or yellowish green mineral; if the acid be now heated, the dolomite will be entirely dissolved with a little of the last mentioned mineral.

In order to obtain the Boltonite as pure as possible for analysis, the following method was adopted. Pieces were separated by the hammer as thoroughly as possible from all other substances; these were subsequently placed in dilute hydrochloric acid, and boiled for some time; the acid being washed away and the substance dried, it was crushed in a mortar to fragments from the twentieth to the tenth of an inch in diameter; these were again introduced into dilute acid and heated for a short while; the acid was thoroughly washed away, and the mineral dried. The small fragments (now like coarse gravel) were placed on a piece of glazed paper, the hand laid flat upon it and the mineral rubbed so as to grind the particles against each other for the purpose of ridding their surfaces of a little cohering silica arising from its partial decomposition; with a small gauze sieve the finer particles are separated, and from that remaining in the sieve we are enabled with the aid of a glass without any difficulty to pick out the pure Boltonite. This method requires a little patience, but no extraordinary care, and however unpromising the original specimens may have been, there is no difficulty in obtaining a material, the results of whose analysis is constant. From a larger selection of specimens than that used, there doubtless could be obtained pieces perfectly pure of some size. After being satisfied with this method of obtaining the pure mineral, three different portions were pre

*This Journal, vol. viii, 2d ser., p. 391.