Popular Science Monthly/Volume 7/September 1875/The Great Iowa Meteor
By Dr. GUSTAVUS HINRICHS.
ON the evening of Friday, February 12, 1875, at twenty minutes past ten o'clock, one of the most brilliant meteors, of modern times illuminated the entire State of Iowa, and adjacent parts of the States of Missouri, Illinois, Wisconsin, and Minnesota. The southeastern portion of Iowa was bright as day, while the great meteor, in descending to the earth, passed from Appanoose County to Iowa County. The meteor, in rapidly moving through the atmosphere, produced a great variety of sounds—rolling, rumbling, and detonations of fearful intensity—which in a large portion of Iowa County shook the houses as if moved by an earthquake.
But three days after the great phenomenon, a meteoric stone, weighing seven pounds,—was found by Miss Sarah Sherlock, while on her way from school—precisely where observers had seen a "glowing coal" descend to the earth. In April and May, while the farmers were cultivating the land, about 400 pounds of meteoric stones were gathered on the meteorite-field of Iowa County. Quite recently two large meteorites have been found, aggregating 120 pounds. But these 500 pounds of meteoric stones apparently are only a portion of a smaller fragment of the entire meteoric body, so that the whole mass falling to the earth, as the great Iowa meteor of February 12, 1875, must have weighed about 5,000 pounds.
Even what has been gathered thus far permits us to rank this meteor among the best observed and richest in meteorites on record. Such are the meteors of Pultusk, Poland (January 30, 1868); Knyahinya, Hungary (June 9, 1866); Orgueil, France (May 14, 1864); Guernsey County, Ohio (May 1, 1860); Parnallee, India (February 28, 1857); and L'Aigle, France (April 26, 1803).
Thinking that so remarkable a meteor and so rich a shower of meteorites deserve the attention of the readers of The Popular Science Monthly, we offer a short description of them, and shall close with a few suggestions in regard to the origin of these bodies, and their place in the grand history of cosmos.
I. The Great Iowa Meteor.—The great Iowa meteor consisted of an elongated, pear-shaped mass of the most dazzling whiteness. The bulk of this mass was about 2,000 feet long and 400 feet in diameter; the narrow white trail was about 4,000 feet long and 40 feet in diameter. This body was posteriorly enveloped by a much less brilliant trail, shading from orange inside to greenish outside, and extending about nine miles along the described path of the meteor. Persons in the track of the meteor saw a brilliant circular disk of white light, surrounded by an orange to greenish halo, the dim light of which was constantly traversed by narrow bands of brilliant white, running from the central disk in irregularly-curved lines toward the circumference. As this body, increasing in brilliancy and apparent magnitude, was rapidly approaching, both men and animals were overcome with fear.
The meteor, when by striking the atmosphere of the earth it became visible, was at an altitude of 150 miles vertically above the little village of Pleasantville, about midway between Kirksville and Milan, in Northern Missouri. Descending at an angle of about 45° toward the earth's surface, it moved a little east of north, gradually deviating more and more toward the east, so as to describe a curve, the concavity of which is turned eastward. This track of the meteor passed a couple of miles east of Centreville and Moravia in Appanoose County, Iowa; almost directly over Eddyville on the Des Moines River; crossed almost diagonally the northeastern (Prairie) township of Keokuk County; passed one and a half mile east of Marengo in Iowa County, and finally exploded over a point three miles southwest of the little station of Norway on the Chicago & Northwestern Railway, over the boundary-line of Benton and Iowa Counties, at an altitude of about ten miles.
While the meteor crossed the northwestern (Prairie) township of Keokuk County, it was seen to divide into two unequal parts, a small eastern portion continuing its motion northeastward, but soon losing its brilliancy, and a seven to fourteen times greater western portion which remained intensely brilliant until its final explosion. It was the smaller portion of the meteor which produced the meteorite shower in Iowa and Amana Townships of Iowa County; hence it is highly probable that several thousand pounds of meteorite, some in pieces of over a hundred pounds, will yet be found east and north of the final explosion of the main portion of the meteor, that is, in Florence Township of Benton County, in Fairfax Township of Linn County, and in Lenox Township of Iowa County. In fact, observers have seen "large glowing coals," as they call them, fall in this region where Linn, Benton, and Iowa Counties meet.
Willie dividing, the meteor produced two tremendous detonations, and, after the main body had crossed the railroad at Marengo, it produced three terrific detonations, which shook the buildings for miles around, so as to create in the residents the fear of an earthquake.
Besides these detonations, the meteor was accompanied with a variety of other sounds, heard over a circular area of 150 miles in diameter. To those farthest away from the orbit it sounded as if their chimney was on fire, and an astonishingly large number of persons missed the sight of the meteor because they hurried to their stoves and flues to check the apparent fire. Those nearer the track heard a prolonged rumbling and rolling sound, which they compare to that produced by the running of a train over a high and long trestle-bridge. Others, still nearer the region of final explosion, hurried up-stairs, thinking that the plastering had fallen on the heads of their children sleeping in the upper story. Many in this same region heard the clank and clatter of heavy, hard bodies striking against each other, or against the hard ground.
II. The Iowa County Meteorites.—The meteorites thus far found occur in an elliptical area stretching from Amana von der Höhe, in Amana Township, to Boltonville, in Iowa Township, a distance of eight miles. The minor axis of this ellipse measures about three miles. The entire meteorite-field of Iowa County thus far covers, therefore, an area of eighteen square miles. In the northwest the largest pieces are found; toward the southeast, the meteorites become gradually smaller. This agrees with their derivation from the minor portion of the meteor. As the entire drift was eastward, the resistance of the air would, to some extent, produce precisely this distribution of the meteorites according to size.
The principal village near the meteorite region is Homestead, a station on the Chicago, Rock Island & Pacific Railroad, about twenty-miles west of Iowa City. This little station became the headquarters
Fig. 1.—Iowa Township, Iowa County, Iowa.
of the "meteor-brokers;" for two dollars a pound had been offered for all these stones. Enormous profits were made, creating a "meteor excitement" in the region.
Fig. 2.—Iowa County Meteorites.
Mineralogy pertaining to my chair of physical science in the Iowa State University, I felt it my duty to furnish the mineralogical cabinets with good specimens of the meteorites which fell in my neighborhood. I have, through the personal and financial assistance of the Hon. John P. Irish, of Iowa City, brought together three collections, the first two of which have been photographed. The subjoined cut is a copy of the photograph of the first collection. It shows the general form of each of the specimens, numbered in the order of their weight. The photographs themselves, in one-fifth natural size, are very excellent, permitting even a close study of the granulations and surface. The above cut gives the specimens in one-seventh of their natural size.
The following catalogue gives the specimens of my collections in the order of their weight. The numbers correspond with those on the map of Iowa Township. No. on the map indicates the "Sherlock Stone," the first one found:
But a few days ago (on June 30th) I received a dispatch from the meteorite headquarters that quite a large specimen had been found. Since, an additional, somewhat smaller stone has been found on the same section of land, namely, on section thirty of the township, directly north of Iowa Township—or about two miles north of the spot A in section six of the map, but a little south of the society village called Amana vor der Höhe. I have visited this place, and been kindly permitted to examine these truly beautiful specimens. The larger meteorite forms an irregular, rounded rhomb, 15 inches diagonal and 8 inches thick; it weighs 75 pounds, or 33.6 kilogrammes, and is completely covered with a black crust, i. e., a complete stone. The smaller meteorite forms an irregular rhomboid, the diagonals of which are 16 and 10 inches, while it is 12 inches thick; it weighs 48½ pounds, or 21.1 kilogrammes. One of its sides has but a secondary crust, so that another piece of perhaps 20 pounds must be found in the neighborhood. The smallest complete stone is in the possession of Mr. William Moerschel; it is a lenticular stone, weighing two ounces only. The largest stone found weighs, therefore, 624 times as much as the smallest!
The two admirable specimens just described belong to the largest meteoric stones on record, as may be seen from the following table, which, however, is probably not quite complete below forty kilogrammes.
The Amana Society has confided these two remarkable specimens to me for study. They appear to have formed but one stone when the meteor first struck our atmosphere.
The number of meteorites thus far found in Iowa County is about one hundred; the total weight is over 500 lbs., or 225 kilogrammes.
The Iowa County meteorites are all alike, bounded by irregular plane surfaces, indicating the usual fragmentary nature of meteorites. They are all covered with a black crust, formed during the cosmical part of their motion through the earth's atmosphere. This crust is not due to fusion, but simply to the heating of the outer layer of the stone to a red heat, as has been proved by Meunier. Indeed, the gray mass of these meteorites turns very readily black by exposure to a red heat. The surface of these meteorites shows all the ordinary impressions of meteoric stones; the finger-marks, granulations, ripples simulating the flow of fused matter, etc. The anterior side is, as commonly, deeper black than the posterior side; the latter has the smaller finger-marks.
These meteorites are exceedingly tough, so that it is difficult to break them up; this is due to the iron grains being partly connected by fibres and folia. Still, the nickeliferous iron is present in detached masses, or occurs sporadically in the stone. Hence these meteorites belong to the great class of Sporadosidères of Daubrée. In this class Daubrée distinguishes three species: those containing much, little, or but very little iron, so that it can only be recognized by a magnifier or a microscope; these species he designates as Poly-, Oligo-, and Krypto-Sporadosidères. Accordingly, the Iowa County meteorites are Oligo-Sporadosidères, that is, meteoric stones containing but little plainly visible metallic iron, in detached grains. I find that these stones contain seven per cent., by weight, of metallic iron. The specific gravity of these meteorites is, therefore, rather low, namely 3.57.
The fracture is very rough and uneven, showing the lustrous metallic iron, and also irregularly rounded spots of lighter gray to white on the dark-gray ground. These rounded stony concretions show very well on a ground surface of the stone; they have given rise to the name Chondrites, introduced by G. Rose, for this class of meteorites. I find that the grains of lighter color contain less of iron silicate, but otherwise are composed of the same minerals.
These minerals are essentially two, namely, Olivine, which is soluble in muriatic acid, and Pyroxene, which is not soluble in this acid.
Besides, the stone contains some troilite, that is, iron sulphide. The following table gives the mineralogical composition of the Iowa County meteorites, according to a number of analyses:
The olivine is the variety known as Hyalosiderite, which contains two atoms of magnesium to each atom of iron. In the pyroxene of these meteorites the same ratio of iron and magnesium obtains; hence this variety is Hypersthene.
The following table gives the result of my analyses of the average composition of the Iowa County meteorites:
A trace of manganese remains with the ferrous oxide—also a small amount of alumina. The trace of sodium is sufficient to give a brilliant line in the spectroscope; the lithium-line, while quite distinct, is not brilliant.
An extended report of my examination of the Iowa County meteorite will be published, as soon as the more careful investigation of the concretions shall have been completed, which examination is delayed for want of material. I am unwilling to sacrifice any of the fine specimens above enumerated for this purpose.
III. The Origin of Meteorites.—The researches of Daubrée and Meunier, of Paris, have demonstrated that meteorites are fragments of one or more planetary bodies, which, by some great convulsion, has been broken to pieces. Furthermore, we possess abundant evidence that the earth, in its structure, corresponds, at different depths, to the different varieties of meteorites: from those without iron (Asydères), through the Oligosidères to those consisting exclusively of nickeliferous iron (Syssydères). Hence if our earth, through the action of some cause, should be broken to pieces, these pieces would be meteorites and describe orbits around the sun similar to and near by the orbit of the earth.
But the cosmical spaces are filled with a very rare, slightly-resistant medium. Hence, the fragments being different in density and in dimensions, would be differently affected by this resisting medium. The smaller fragments and those of less density would lose their velocity of revolution around the sun more rapidly than those of greater size and higher density. In other words, all fragments would, while revolving around the sun, also descend toward the same, bat at different rates: the smaller and lighter fragments would sink faster than the larger and heavier.
These terrestrial meteorites would, therefore, gradually reach the orbits of the inner planets. On Venus first would appear meteorites composed of the rocks of our earth's superficial crust, limestone, shales, quartz, granite, serpentine, etc. These would be associated with small meteorites of more dense materials derived from the deeper portions of the earth. At a later period, Venus would receive terrestrial meteorites from deeper portions of our earth, corresponding to Oligosidères. These would also be associated with small meteorites of denser materials, thus foreshadowing the third meteorite era, in which the dense masses of the interior metallic core of our earth would have sunk far enough toward the sun to reach the orbit of Venus. The mechanical problem herein involved I pretty completely solved about ten years ago.
Now, it is furthermore well understood that it will be a long time before the earth is so broken up; for celestial bodies pass through their cosmical cycles in times somewhat proportional to their magnitude. Therefore, long before the earth meets this, her final doom, the moon will have been so broken up that her "lunar meteorites" will have been placed in the mineralogical museums, I trust, at less than "two dollars a pound."
Accordingly, we must look for the origin of our meteorites up away from the sun. We believe that they are fragments of some of the more minute asteroids of which hundreds yet continue to move between Mars and Jupiter. The frequent stony meteorites now falling, therefore, probably are the forerunners of a period of frequent iron meteorites, corresponding to the deeper portions of the same minute planet, the exterior layers of which have been reaching us quite frequently of late. The meteoric irons of our cabinets must have belonged to another asteroid, broken up at an earlier date than the asteroid now yielding the large and frequent crops of meteoric stones.
This is not the place for a more complete development of this view. But, as every reader inevitably would ask the question, "Whence these meteorites?" we deemed it best to give our answer.
The nebular theory fully accounts for the planetary system in its glory; but this harmony is finally followed by a breaking up and destruction of each body, which then as meteorites continue to move, truly cosmical fossils, until they find a temporary rest on the orbs which are nearer the grand centre of our world, the glorious sun.