Popular Science Monthly/Volume 58/February 1901/A Century of the Study of Meteorites
|A CENTURY OF THE STUDY OF METEORITES.|
CURATOR OF GEOLOGY, FIELD COLUMBIAN MUSEUM.
THE close of the nineteenth century will mark the end of the first century of the study of meteorites. Up to the beginning of this century the attitude of scientific men toward the accounts of stones reported to have fallen from the sky was in general one of scorn and incredulity. Thus an account prepared with great care by the municipality of Juillac, France, telling of a stone shower which occurred there in July, 1790, was characterized by Berthelon at the time as "a recital, evidently false, of a phenomenon physically impossible" and "calculated to excite the pity not only of physicists but of all reasonable people." Bonn, in his Lithophylacium Bonnianum, refers to the Tabor, Bohemia, meteorite which fell in 1753, as "e coelo pluvisse creduliores quidam asseverant." Chladni, writing in the early part of the century, speaks of many meteorites which were thrown away in his day because the directors of museums were ashamed to exhibit stones reported to have fallen from the sky. President Jefferson when told that Professors Silliman and Kingsley had described a shower of stones as having taken place at Weston, Conn., in 1807, said: "It is easier to believe that two Yankee professors will lie than to believe that stones will fall from heaven."
The change of opinion on the part of intelligent and especially scientific men, which took place at the beginning of this century, was due largely to the investigation by the French Academy of the shower of stones which fell at L'Aigle in 1803. This investigation established so absolutely the fact of the fall to the earth at L'Aigle of stones from outer space that scientific men were logically compelled to give credence to the reports of similar occurrences elsewhere. Further, the papers of Chladni and Howard published about the same time, strenuously urging that other masses reported to have fallen upon the earth could not, because of their structure and composition, be of terrestrial origin, had much to do with fixing the growing faith that solid cosmic matter not of terrestrial origin does at intervals come to the earth. Since this beginning the study of meteorites has been one of constantly widening interest and purport.
The essentially distinguishing features of meteorites were early made out. Howard in 1802, from a chemical investigation of various "stony and metallic substances which at different times are said to have fallen on the earth, also of various kinds of native iron," drew the conclusion that a content of nickel characterized most such bodies. He also found that the meteoric stones were made up chiefly of silica and magnesia and that the iron sulphide of meteorites was distinct from the terrestrial mineral pyrite. He further noted the chondritic structure as characteristic of many of the meteoric stones. The correctness of his observations was soon confirmed by analyses made by Fourcroy, John, Klaproth and others. In 1808 Alois von Widmanstätten, by heating a section of the Agram iron, brought out the figures which have since proved so characteristic of meteoric irons in general and which are now known by his name. Thus the data were early at hand for distinguishing meteorites from terrestrial bodies and it soon became possible to collect the 'sky stones' even when they had not been seen to fall. Systematic efforts for the collection of these bodies were not put forth, however, for many years. Up to 1835 there were only fifty-six different meteorite falls represented in the Vienna collection, and in 1856 only one hundred and thirty-six. Up to 1860 those of the British Museum collection numbered only sixty-eight and those of the Paris collection only sixty-four. The studies of these bodies during the first half of the century were made, therefore, upon a relatively limited number. The earlier investigations were chiefly chemical in character, various elements being discovered in succession. Manganese was discovered in the stone of Siena by Klaproth in 1803, chromium in the stone of Vago by Laugier in 1806, carbon in that of Alais by Thenard in 1808, chlorine in that of Stannern by Scheerer in the same year and cobalt by John in the Pallas iron in 1817. The number of elements discovered since has brought the total up to twenty-nine, none being found, however, which are not already known upon the earth. Many of the chemical compounds of meteorites were early isolated and their identity with terrestrial minerals established. Count Bournon showed in 1802 that the transparent green mineral accompanying the iron of Krasnoyarsk was olivine. The same mineral was found in other meteorites by later observers, and Rose was able in 1825 to make angular measurements of the crystals which showed them to be identical with those of terrestrial olivine. Laugier separated chromite from the stones of Ensisheim and L'Aigle in 1806. Augite was recognized by Mohs in the stone of Stannern in 1824 and by Rose in that of Juvinas in 1825. Haüy recognized a feldspar which he thought to be orthoclase in the stone of Juvinas in 1822, but three years later Rose showed it to be plagioclase; and the existence of orthoclase in meteorites has yet to be proved. Continued investigations of the compounds found in meteorites up to the present time have resulted in the detection of at least twenty-one whose composition is certain, besides several of a somewhat problematic nature. Of these compounds seven have been found to differ in composition from any known terrestrial substances. The character of these indicates the complete absence of water and of oxygen in any large amount from that portion of nature's laboratory where meteorites are formed. Important investigations as to the gases occluded by meteorites were begun by Boussingault in 1861 and have been continued by Wright, Ansdell, Dewar and others. It has been proved that large quantities of hydrogen, as well as carbonic acid gas, are contained in these bodies, under pressure greater than that of the earth's atmosphere. These investigations led further to the spectroscopic study of meteorites by Vogel, Wright and Lockyer. The spectra thus obtained when compared with those exhibited by comets showed striking resemblances, which have led to a growing belief among scientific men in the identity of origin of comets and meteorites. Lockyer has indeed pushed this conclusion to the point of believing that "all self-luminous bodies in the celestial spaces are composed either of swarms of meteorites or of masses of meteoritic vapor produced by heat," and he draws from this many important deductions relating to the origin of the stars, comets and nebula?, and the physical conditions prevailing in them. It will remain for the twentieth century to test the correctness of such conclusions, but the facts already brought out have considerably shaken the confidence hitherto placed in the nebular hypothesis. Another interesting result of the century has been the establishment of a general similarity between shooting stars and meteorites. This idea was first suggested by Chladni in 1798, but it has remained for Newton, Adams and Schiaparelli to give it shape and proof. The general verdict of science is now in accord with the belief of Newton, "that from the faintest shooting star to the largest stone meteor we pass by such small gradations that no clear dividing lines can separate them into classes." Moreover, the longexisting belief in le vide planétaire, space filled only with a mysterious fluid called ether, has been shown to be untenable. Careful records and estimates have shown that 20,000,000 cosmic bodies large enough to produce the phenomena of shooting stars are encountered by the earth daily. The number of these bodies existing in space must be, therefore, beyond all calculation, and their existence implies that of smaller particles in sufficient number to form a widely pervasive cosmic dust. Many remarkable meteorite falls have occurred during the century. Beginning with the stone shower of L'Aigle in 1803, when 2,000 to 3,000 stones fell, no less than eleven such showers have been recorded. In the shower of Pultusk, Poland, which occurred in 1868, 100,000 stones are estimated to have fallen, their total weight reaching over 400 pounds. In the shower at Mocs, Germany, in 1882, more than 3,000 stones fell. In our own country about 750 pounds of meteoric matter fell at Estherville, Iowa, in 1879, and several thousand stones fell over an area nine miles in length and one mile wide near Forest City. Iowa, in 1890. Many oi these falls have been marked by extraordinary phenomena of light and sound, making them events never to be forgotten by those who witnessed them and worthy to be reckoned among the most remarkable natural occurrences of the century. About two hundred and eighty-five actually observed meteoric falls is the total recorded during the century. It is a remarkable fact regarding the nature of the material fallen that only five of these have been of meteoric irons. One of these irons fell at Mazapil, Mexico, during the star shower of November, 1885, at the time when the return of Biela's comet was looked for, and was thus considered an occurrence corroborative of the already suspected relationship among comets, shooting stars and meteorites.
The indifference to the collecting of meteorites which characterized the early part of the century has given place in its latter days to an extraordinary diligence in the search for these bodies. One meteorite has of late acquired a value equal to four times its weight in gold and several can be sold for two and three times their weight by the gold standard. The meteorite collection of the Natural History Museum in Vienna has for many years been the leading one. What it has cost to build it up may be known from the fact that it is considered the most valuable of any single collection in that great treasure house. Representatives of over five hundred meteoric falls are exhibited in this collection, and the meteoric matter has a total weight of seven tons. The collection of the British Museum of Natural History is nearly as large, while at Paris, Berlin, St. Petersburg and Calcutta, together with Washington, Chicago, Cambridge and New Haven, in our own country, are gathered extensive and important collections. The establishment of such large collections has for the first time put the study of meteorites on a satisfactory basis and given lively hope that important truths will be discovered by researches thus made possible. The general similarity of the stony meteorites to the basic volcanic rocks of the earth has been established, and similarity of many physical structures such as brecciation, slicken-sided surfaces and veins has been proved. The chondritic structure and the crystalline structure represented by the Widmanstätten figures are, however, so far as is yet known, peculiar to meteorites, and it will remain for the twentieth century to discover what these structures mean. Classifications of meteorites based on their mineralogical and structural characters have been established, and important differences among meteorites shown, in spite of their family resemblances. It would be idle perhaps to recount, as might be done, many theories regarding the nature and origin of meteorites which have been found untenable as a result of the century's study. The theory of the lunar origin of meteorites had at times such able supporters as Laplace and J. Lawrence Smith. Other able observers have believed meteorites to be material ejected at some past period from the earth's volcanoes; some have regarded them of solar origin and still others as fragments of a shattered planet. All of these theories may be said to have been proved fallacious. The discovery reported by Hahn in 1880 of remains of sponges, corals and plants in meteorites excited for a time eager inquiries into the possibilities of proving by the study of meteorites the existence of life outside our own globe. No satisfactory evidence of the existence of extra-terrestrial life has, however, as yet been obtained from meteorites. The most positive and enduring results of the century's study may, therefore, perhaps be summed up as the establishment of the fact of the fall of solid cosmic matter to the earth and a sufficient knowledge of its nature to distinguish it from matter of terrestrial origin. Satisfactory conclusions as to the origin of this matter and its relations to the visible bodies of the great outlying universe remain yet to be drawn.