Page:Popular Science Monthly Volume 17.djvu/363

Rh 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