In nearly every instance where these disturbances have been described some mention is made of the quantity of the material transported by the atmosphere. Nevertheless, it is exceedingly difficult to make any definite estimate in this direction, as no actual measurements have been made by any of the observers. But a number of the accounts are such that comparisons can be made between the phenomena described and some other instances of dust transportation which have come to the writer's notice, and which have furnished some quantitative estimates. The results of such comparisons are here given for what they are worth. In several cases the effect of the dust on the transparency of the atmosphere is noted. It is thus stated that—"It gives the sun a sickly color."—"It is dense enough to obscure the mountain ranges from view" (at a distance of from five to ten miles),—"It is sufficient to allow the sun being viewed with the naked eye."—"Immense quantities of sand and dust filled the air, until the sun became so obscure that it could only be seen as a round ball, at which one could gaze with impunity."
During a high wind on the 25th of March, 1895, following a dry season, the atmosphere over the northern part of Illinois and over a part of Iowa had an appearance which corresponded to the instances here described. The storm lasted about three hours, and during that time an apparatus for collecting dust from the atmosphere was suspended at an elevation of about a hundred feet above the ground back of the bluffs of the Mississippi River at Rock Island, Ill. This apparatus was so arranged that dust could not be taken from a current of air more than a tenth of a square foot in cross-section. It is possible that the actual current was not more than a tenth as large as this. The quantity of dust collected was about two ounces. The wind velocity for the three hours was thirty miles per hour. This indicates that the atmosphere on that day carried a load of one hundred and sixty, or possibly sixteen hundred, tons of dust to the cubic mile of air.
Some of the notes refer to the accumulation of dust and sand in dwelling houses and other buildings, viz.: "Merchants closed their doors to protect their goods" (from the dust).—"The quantity of sand swept from houses (by housekeepers after a storm) showed the severity of the storm the two previous days. The sand penetrated every nook and corner."—"The pattern of the carpet may be obliterated; drifts have been formed on the floor from one to two inches in depth."—"The dust filled every residence completely [!] covering up everything while it lasted."—"The wind hurled a few quarter sections [!] of rich loam into the residences and business houses."
Blown dust is a general and familiar nuisance to housekeepers over the entire West. A minimum estimate, verified by direct