SCIENCE LETTER FROM FRANCE. 75 
decomposition. As the air is purer after being washed by rain, so in dry weath- 
er and especially in cities, the atmosphere is a veritable dust-bin; we are sensi- 
ble to the existence of these particles of attenuated matter; in breathing them 
they disgust us, and in falling and remaining on clothing and furniture they 
demonstrate not only their presence but their plenitude. Admit a sunbeam into 
a-darkened room and the molecules will be revealed like nebule; yet the num- 
bers we perceive, are perhaps but the minimum of what exists, for after the naked 
eye and the microscope there are minutiz which dance still. Much of this atomic 
debris is of inorganic origin, and a great deal is derived from animal and vegeta- 
ble sources; the renowned experiments of M. Pasteur have demonstrated, that among 
these atomies which live, move, and have their being in the air, are germs or 
spores of fermentation and decomposition, that is to say, the seeds of disease and 
death. Showers of dust impalpable as flour, and sometimes red as blood, have 
fallen in several parts of the world, astonishing or frightening, as the populations 
are superstitious or cultivated; these showers are simply silicious particles whipped 
up to the superior regions of the atmosphere, and driven along by aerial currents ; 
such particles have been lifted in Guiana and showered on New York, the Azores 
and France, as Ehrenberg detected therein animalcule and shells, peculiar to 
South America. Over the summits of the high mountains of the latter country, 
the atmospheric currents are ever charged with silicious powder, and in parts of 
Mexico, the crests of mountains act as veritable bars, and compel the deposition from — 
these air streams of the dust, and which accumulate in the valleys to the depth of 
ninety yards. Geology recognizes these atmospheric deltas. The foam of waves 
as they dash against the coast, is pulverized into feathery pellicles, which float 
sky-ward with a trace of saline matter and that a sea breeze carries far inland. 
Space contributes. as well as earth and ocean to the production of aerial dust ; 
when meteorites and falling stars are rendered luminous and incandescent by their 
rubbing against strata of air in their vertiginous flight, they part with quantities 
of their metallic elements in the form of powder, iron, nickel, and cobalt, sub- 
stances that Nordenskiold has gathered on the virgin snow of the Polar regions. 
When atmospheric dust, whether collected directly on a sheet of paper, or from 
the sediment of snow and rain, is probed by a magnet, the tiny particles of iron 
attracted, have all a spheroid family likeness, resembling furthermore iron filings 
if melted in a flame of hydrogen or the extinguished sparks that fall on striking 
an ordinary flint and steel. Nay more, similar atoms of meteoric iron have been 
traced in the Lower Lias formation, geology thus affording evidence, that as now, 
so before the appearance of man on earth, atmospheric dust existed. ‘The air is 
a vast store house of animalcules; expose a solution of some organic substance to 
the atmosphere for twenty-four hours, it will be speedily inhabited by myriads of 
infusoria, rolling and tumbling, yet so small that hundreds of them if placed in a 
row would not forma line in length. These worms resemble little eels An- 
alogous animalcules induce decomposition and fermentation, for the latter cannot 
take place unless the organic matters be in contact with the air, to receive the 
