sible that the stifling sensations felt in a dust-laden atmosphere are the results of a cumulative stimulus on the nervous system, and a smaller quantity might produce similar effects. No doubt there is also a subjective factor which will modify estimates on this line.
Lastly, an estimate, or rather a measurement, has been made on the quantity of sand carried in such storms as are recounted in the following items: "The sand is blown about in such quantities that it is not possible to keep one's eyes open."—"A man venturing into a whirlwind of sand invariably returned in a few minutes with his face bleeding with hundreds of cuts."—"Clouds of sand were driven through the air by a high wind, obscuring all objects and rendering existence almost impossible (sic) for man and beast."
In 1886 the writer had the opportunity to be in the midst of such flying sand on the Western plains, and to make some observations on the quantity borne by the air. The storm was not as severe as those described in the above paragraphs, nor did it carry as much drift, for neither was the author's facial integument punctured nor did he experience any apprehensions as to the possibility of continued existence. But there was enough of sand in the air to deposit one ninth of an ounce during fifteen minutes in a vial with an aperture measuring one tenth of a square inch turned to the windward. A velocity of twenty miles per hour was probably not exceeded where the receptacle was placed, and this would make the load carried equal to nearly thirty thousand tons per cubic mile.
To sum up: The estimated loads of sand and dust that may be carried by the atmosphere range from 150 to 126,000 tons per cubic mile of air, or from 0·0009 to 0·77 grammes per cubic foot.
|Estimate on a thick haze||160||0·0009||0·031|
|Lowest estimate from accumulation in dwellings||225||0·0013||0·048|
|Estimate on opaque dust clouds||2,000||0·012||0·434|
|Estimate on forming sand drifts||6,000||0·037||1·30|
|Estimate from effect of dust in the air on breathing||20,000||0·123||4·34|
|Estimate from a quantity of sand collected in a storm||30,000||0·184||6·49|
|Highest estimate from a quantity of sand in dwellings||126,000||0·77||27·29|
With these figures and the data on the duration and on the frequency of sand storms in the western part of the United States, it seems possible to form some idea of the total amount of work performed by such storms over this territory. It is not believed that the data presented justify any great claims for exactness