ATMOSPHERIC DUST. 



3+9 



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 



Fig. 1. Crystals obtained by evaporating to Dryness a Drop of Snow-water. 



(500 Diameters.) 



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 pro- 

 duces an affection which Dr. Riembault, of St.-Etienne, has designated 

 as the carbonaceous obstruction of the lungs of miners. He has dis- 

 sected the lungs of workmen who had labored in the mines for a 

 greater or less length of time, and has found that this pulmonary ob- 

 struction 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 yeai's, and a blackness ap- 

 proaching, 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- 



