Winckell and Miller— Bust fall. 599 



Aet. XXVIII.— The Dustfall of March 9, 1918; by A. N. 

 Winchell and E. R. Millee. 



Some of the snow which fell at Madison, Wisconsin, 

 on March 9, 1918, contained sufficient foreign material to 

 change its color from white to a light brown or yellow, 

 It was observed nnder conditions which permitted a close 

 study and the collection of some evidence and data 

 regarding the material. It is the object of this note to 

 put these data on record, and to discuss the quantity, 

 nature, and probable source of the coloring matter. 



The colored snow came down at Madison in the form 

 of moist snow mixed with sleet, during the passage of 

 an unusually intense and fast moving cyclonic disturb- 

 ance. It fell from 11 :30 a. m. to 2 :30 p. m., 90th meridian 

 time, but the proportion of coloring matter is believed 

 to have been greater toward the end than at the begin- 

 ning. The moist snow and sleet were preceded by rain, 

 from 9:30 a. m. to 11:30 a. m., which froze as it fell, and 

 remained as a sheet of ice about % inch thick on trees, 

 wires, etc. The moist snow and sleet were followed by 

 dry snow from 2 :30 p. m. to 9 :30 p. m. Neither the ice 

 nor the dry snow contained an appreciable amount of 

 coloring matter. 



At the time of the storm the snow and sleet were 

 observed to have a light reddish brown color, not only by 

 the Weather Bureau observers, but also by others, some 

 of whom called upon the Weather Bureau office for an 

 explanation of the " dirty snow" while it was yet falling. 

 The discoloration was still more easily seen after the pure 

 white dry snow had begun falling and drifting into the 

 depressions in the darker layer. On the second day fol- 

 lowing, when the snow began melting the dust was left 

 on top of the snow. 



Area of fall. — The evidence obtained as to the area 

 covered by the dusty snow fall is admittedly incomplete 

 and inconclusive. Inquiries were sent immediately after 

 the fall to a number of Weather Bureau officials in cities. 

 The replies from most of these indicated that the con- 

 tamination of the snow by city smoke, dust, and ashes had 

 precluded any possibility of recognizing the colored 

 snow. Only Mr. J. H. Spencer at Dubuque, Iowa, and 



Am. Jour. Sci. -Fourth Series, Vol. XLVL No. 274.— October, 1918. 

 26 



