Jacques Wardlaw Redway

“ The surface is almost infinitely great in comparison. Now, the electric charge of a dust particle, condensed on its surface, is of the same kind as that of the earth. Therefore they mutually repel. It is only fair to add that the theory of the electrification of dust is not fully substantiated. ”

“ When the velocity of the wind is doubled its carrying power is increased sixty-four fold. In regions of loose rock waste the wind becomes a wonderful physiographic factor. The broad, intermontane valleys of the plateau region have been filled with rock waste, much of which is wind-blown; and the floors of the deeply filled valleys have been made level by wind-blown dust. The plains to the eastward of the Rocky Mountains are deep with wind-blown dust. More dust and rock waste is deposited in the rivers of this region than they are able to carry. ”

“ The wind-blown dust from these consists chiefly of loose dirt, paving material, garbage, finely pulverized horse dung, and foliage dust. The dust carried by winds blowing over areas of orchard and shrubbery usually contains the spores of fungi, pollen in season, the spores of various moulds, the eggs of insects and the dust scales of moths. Winds blowing over swampy areas are apt to have a generous content of the micro-organisms common to swamps. Dry air contains the spores of micro-organisms; moist air is often rich in the organisms themselves. ”

“ The particles themselves are too small to be discerned by any mechanical method at present known. En masse they reflect enough sunlight to reveal their existence, but not their form nor their constitution. In part, and probably to a great extent, they constitute the overhead effect noted by observers for more than six thousand years—the sky. An estimate of the size of such dust particles cannot be made with any degree of accuracy. It is safe to say that they are much smaller than the smoke particles that escape from the burning end of a cigar. ”

“ John Aitkin, the highest authority on the subject, has shown that clean air contains from 3000 to 5000 visible dust particles per cubic inch. The air of schoolrooms and public buildings with undressed wood floors carries from 60,000 to 80,000 particles which are visible under the high power of a microscope, and an unknown number which can be counted only when amplified in size by the condensation of moisture upon their surface. ”

“ Sulphur dioxide is a gas and is not to be included in the dust content of the air. But the intense heat of combustion has separated it from the combination in which it existed. The chemical affinity of the nascent gas is strong, and in the air it is apt to enter into combination again with dust particles of basic character, the resulting combination forming nuclei favorable to rapid condensation. ↑ Volcanic “ash” is not a product of combustion. It is the convenient name applied to lava blown into fine dust by the expansive force of steam, or by other forces. ”

“ In regions where smokeless fuel is used there practically is no smoke problem, and the pollution of the air is confined almost wholly to wind-blown dust and to local sources of pollution. In localities swept by sea winds, salt derived from wind-whipped spray is usually a factor in the floating dust. ”

“ Condensation does not take place so readily—in other words, the dust particles are indifferent nuclei. A thick fog condensed on nuclei of an indifferent sort may be “eaten up” by a slight rise in temperature; it may rain itself to pieces by a drop in temperature.
Sources of Atmospheric Dust.—Aside from the dust picked up and carried by the winds, there are well-defined sources of floating dust that must be considered. Cosmic, or meteoric dust, is not born of the earth; it is gathered by the earth from space. Large particles fall to the earth ”

“ They are essentially different from the metallic particles of smeltery dust, emery-wheel dust, and brake-shoe dust, which also are metallic. The cosmic dust of non-metal character cannot be recognized with any degree of certainty; indeed, recognition of any sort of dust whose particles are less than a micromillimeter is difficult. The gathering of cosmic dust seems to be constant rather than sporadic. ”

“ The suspended matter of combustion products has been measured at times. Systematic measurements both of suspended matter and of matter which is brought to the ground by rainfall have been made in various parts of England, at regular stations. ”

“ The amount varied from a few hundred tons per year on each square mile to nearly 6000 tons per square mile. Measurements in several manufacturing districts of Pennsylvania showed an average of about 1900 tons per square mile per year falling to the ground. ”