of the formation of beds by the settlement of the dust, covering the largest mountains, as Popocatepetl and Orizaba, rising to the height of about 12,000 feet on the slopes and reaching a thickness in the valleys of from 250 to 325 feet. These formations are occasioned by whirlwinds of dust which are frequent on the Mexican plain, and are stopped by the elevated chain of the mountains, as the mud in a river is stopped by a sand-bar. The action of the prevailing winds in other parts of the globe promotes the formation of similar deposits, which may be

called aërial lands.

These are the dusts of the lower regions of the atmosphere. But the air contains other particles in the most minute degree of division. The waters of the sea, impinging on the coast in waves, are broken into thousands of particles which are taken up and evaporated by the winds. The saline residue of these particles adds a new element to the atmospheric dust; the vapors furnished by the sea go to the formation of clouds and fogs. Rising beyond the regions of ordinary clouds, these vapors ascend to the colder strata, where they are converted into a dust consisting of minute crystals of ice which form the cirrhus clouds and the ice-fields of the upper regions. These masses of frost, which can only be distinguished when they are approached by a balloon, but the existence of which is well established, are agents in the formation of halos and parhelia, and descend in cold winds to the surface.

FIG. 2.-CORPUSCLES EXTRACTED BY THE MAGNET FROM THE SEDIMENT OF RAIN-WATER AT SAINTE-MARIE-DU-MONT, MANCHE. (500 Diameters.)

If we pass these heights, into the extreme limits of the atmosphere, we shall find ourselves in the presence of dust from a new source-of that which is furnished by the combustion of incandescent aërolites. The fruits of the study of meteoric astronomy prove that the surface of the earth is continually receiving cosmic materials either in the form of meteorites or shooting-stars, or of an impalpable dust. A ship passing to the south of Java in January, 1859, was assailed by a very fine ferruginous dust. Ehrenberg examined some of it with the microscope, and found that it was formed of melted globules of oxide of iron, and did not hesitate to regard it as consisting of particles of a mass of meteoric iron, which had been melted off by the operations of atmospheric friction. In other cases the particles may originate in the disintegration of the substance of the meteors, when the soluble salts. with which they are cemented are dissolved by atmospheric moisture, as Daubrée observed in the case of a meteorite at Orgueil. Showers of fire have been mentioned, or of sparks which seem to be formed of

the incandescent dust of aërolites. Baron Reichenbach collected on the summit of Lahisberg a black ferruginous dust containing traces of nickel and cobalt, which incontestably indicated its cosmic origin. Mr. Nordenskjöld collected a similar dust from off the snow of the polar regions.

For several years I have paid attention to the study of atmospheric dust, and believe that I have proved that more or less considerable quantities of dust derived from cosmic bodies are constantly present in the air. The greater part of my experiments have been performed in the meteorological observatory of Sainte-Marie-du-Mont, Manche, where M. Hervé-Mangon has placed the resources of his establishment and laboratory at my disposition. I have endeavored to collect large quantities of dust, so that I might carry on micro

scopic and chemical analyses with precision. For this purpose I

used a surface of paper of two square metres, which I exposed horizontally to the air; I collected from it the dust which fell from the air, sweeping it up with a small brush. I called this apparatus a dusttable. The weight of the dust collected upon this surface at SainteMarie-du-Mont varied from two to nine milligrammes (.03 to .14 grains troy) in twenty-four hours. The particles shown in Fig. 1 represent minute grains of magnetic oxide of iron, which were drawn out from the dust by the magnet. They are greatly magnified, their real diameter being only of a millimetre ( of an inch).

If we evaporate considerable volumes of rain-water, we shall obtain a sediment which represents the air-dust; if, then, we draw a magnet through this sediment, we shall nearly always find little globules of magnetic oxide of iron in it. Fig. 2 represents some of these globules, which I extracted from one hundred quarts of rain-water at Sainte-Marie-du-Mont.

We can distinguish several of these grains which have the form of spherules, or granules that have undergone fusion. The sediment from rain-water collected in Paris at the School of Bridges and Highways at the Trocadéro and the dust collected in one of the towers of Notre Dame gave identical results (Fig. 3).

FIG. 3.-CORPUSCLES EXTRACTED BY A MAGNET FROM THE DUST BROUGHT IN BY THE WIND IN A TOWER OF NOTRE DAME WHICH 18 CLOSED TO VISITORS. (500 Diameters.)

These facts prove conclusively that the air holds in suspension minute microscopic particles of oxide of iron, some of which assume the form of well-defined spherules.

Similar spherules may be found everywhere in the dust of the air and in rain-water and snow-water. I have found them in the sedi

ment of snow-water collected at the height of 8,800 feet on Mont Blanc (Fig. 4). Since I have called attention to the existence of these ferruginous bodies in the air, several men of science have confirmed my observations, particularly M. Yung, of the University of Geneva, and MM. Schoenaur and Pierre Miquel, who have pursued the study of the

FIG. 4.-CORPUSCLES EXTRACTED BY THE MAGNET FROM THE SEDIMENT OF SNOW-WATER ON MONT BLANC, 8,800 FEET ABOVE THE SEA. (500 Diameters.)

air-dust at the observatory of Montsouris under the direction of M. Marie-Davy.

Whence are these ferruginous particles derived? The spherules have been melted: we can prove this by burning particles of iron and observing them under the microscope (Fig. 5); those which fly off on the striking of a flint are like them (Fig. 6). The spherules we are considering are probably derived from the showers of fire that escape

FIG. 5.-GLOBULES OF MAGNETIC OXIDE OF IRON OBTAINED BY BURNING FINE IRON FILINGS IN A HYDROGEN FLAME. (500 Diameters.)

from incandescent meteorites. I have been confirmed in this view by observing with the microscope the crust of the aërolites in the collection of the Museum of Natural History, in which were perceived rounded grains having considerable resemblance to those we have just noticed. Moreover, the magnetic particles withdrawn from atmospheric sediments have given on analysis reactions indicating the pres

FIG. 6.-SPHERICAL GLOBULES OF MAGNETIC OXIDE OF IRON OBTAINED BY COLLECTING THE SPARKS STRUCK OFF BY A FLINT. (250 Diameters.)

ence of nickel; of a character, consequently, to cause them to be regarded as partaking of the nature of meteorites. It may be objected that metallurgical operations and the production of oxides in iron-works give rise to similar ferruginous corpuscles. This is true; but how can we explain the presence of the spherules in geological formations that have not been worked over, where they must have been left previous to the existence of man on the earth? M. Stanislaus Meunier and I have found in the grits below the Lias, in the micaceous slates of the

Trias, magnetic globules like the spherules which now fall from the atmosphere upon the earth; we may, according to our theory, consider them fossil meteorites.

Beautiful and peculiar crystalline forms (Fig. 7) are obtained when a drop of rain-water or snow-water is evaporated to dryness, the substance of which consists of the nitrate of ammonia contained in meteoric waters.

The dusts that are produced by man in works of industry expose him to terrible dangers. Stone-dressers breathe very minute particles of grit

which perceptibly injures the lungs; the dust of white-lead, and that of the arsenite of copper, which is used to color cloths and papers, have often produced genuine poisonings. The dust of coal, with which the galleries of coal-mines are filled, is breathed by the miners, and produces an affection which Dr. Riembault, of St.-Etienne, has designated as the carbonaceous obstruction of the lungs of miners. He has dissected the lungs of workmen who had labored in the mines for a greater or less length of time, and has found that this pulmonary obstruction goes on continually increasing till it becomes very dangerous. Sections of the lungs of miners show a gradual progress of coloration, from the fresh, rosy color of the lungs of a person who has always lived in the open air, to gray after a few years, and a blackness approaching that of the coal itself after forty years of labor in the mines. The dust of coal in the mines, when raised up and ignited, either by a blast or by the burning of a little carburetted hydrogen, has sometimes spread fires to great distances in the galleries, burning the workmen and producing terrible catastrophes. M. Galloway has made some impor

tant researches on this subject, and has shown that, even if the dust of coal is not directly inflammable, it becomes very combustible when the atmosphere contains traces of carburetted hydrogen. Other dusts are directly combustible, and sometimes produce genuine catastrophes by the fact of their suspension in the air. In 1869 a sack of starch was accidentally thrown down from the top of a staircase in the Rue de la Verrerie, Paris; it burst and scattered through the air a cloud of dust which took fire from the contact with a gaslight at the bottom of the stairs, and caused an explosion. M. Berthelot has observed that special conditions of mixture are required for the actual production of such explosions, and that a hundred cubic metres of air, containing about thirty kilogrammes of oxygen, will completely burn twentyseven kilogrammes of starch-powder, or eleven kilogrammes of coaldust. The terrible explosion in the flour-mills at Minneapolis, Minnesota, in May, 1878, was of a similar nature with the explosion of the starch in the Rue de la Verrerie.

PRE

THE FOSSIL MAN.

BY HENRY W. HAYNES.

REHISTORIC Archæology, the latest-born of the sciences, like her elder sister Geology, has lived through the successive stages of scornful denial, doubt, and unwilling assent, and has finally won for herself substantial recognition. The "antiquity of man" is now an established fact. Even its most strenuous opponents are forced to concede that there are proofs of his existence during a lapse of time far exceeding the limits of the previously approved chronology. For somewhat of the suspicion with which this result has been received, certain of its advocates may have themselves to blame. Where absolute chronological determinations were of necessity impossible, and where, even at the present stage of the investigation, only general approximations can be reached, it was at least injudicious to startle received opinions, and to arouse prejudices, by asserting for mankind an antiquity of hundreds of thousands of years. Moreover, the great name of Cuvier was held up as a barrier in the path of those who claimed to have discovered proofs of man's existence under geological conditions differing from the present. Cuvier, however, never denied the possibility of finding "the fossil man"; he only questioned the sufficiency of the evidence of his existence which had been brought under his notice, and with great reason, in view of the numerous instances in which pretended fossil human bones had turned out to be those of animals, or even merely natural formations.

Many have been the definitions given of the term "fossil”; but