hail and drip impressions 363 



Hail Impressions 



In the experimental work of the writer, spherical and elliptical pieces 

 of ice were projected with considerable initial velocity from a height of 

 about twelve feet into a tray filled with mud of the same character as that 

 used for making the rain-drop impressions. The mud prepared was given 

 considerable consistency, as it was found that in very soft and fluid mud 

 the hailstones became buried and the depressions ultimately nearly dis- 

 appeared. Hail impressions are deeper and have higher margins than 

 are those made by rain-drops. The depressions are of the shapes of the 

 pieces of ice in cases where these descend perpendicularly. If the hail- 

 stones have horizontal components in their descent, the depressions pro- 

 duced are of elliptical outlines and are deeper and have higher rims on 

 those sides toward which the pieces of ice were directed. As in the rain- 

 drop impressions, the depths of the depressions and the heights of the 

 rims are controlled by the sizes of the hailstones, the force with which 

 they fall, and the character of the mud. Impressions of this origin can 

 also become of far greater diameters than is the case for rain-drop im- 

 pressions, as hailstones the size of a pigeon egg are known to be quite 

 common, and in a big hailstorm in Kansas the past summer hailstones 

 in excess of half-pound weight were reported. It is known that impres- 

 sions of at least a couple of inches in diameter have thus been formed. 

 It is probable that large hailstones would produce impressions in muds 

 overlain by shallow water, although under such conditions considerable 

 mud is stirred up which on settling reduces the de^Dths of the holes. 



Drip Impressions 



Drip impressions, in the writer's observations, appear to be more com- 

 mon than are those made by rain-drops. The beginning of a rain will 

 fall in most cases on dry ground, on which it is well nigh impossible to 

 form impressions. Continued rain destroys those which were formed in 

 the beginning. The closing of a rain rarely makes impressions, as the 

 mud flats are then very soft and are more or less covered with water, 

 making the formation of impressions essentially impossible. Dripping 

 from trees continues for a long time after rain has ceased falling, and the 

 falling drops at some time find the mud in an extremely favorable con- 

 dition for receiving impressions. 



Drip impressions are similar to rain-drop impressions, but the maxi- 

 mum dimensions as well as the average dimensions appear to be larger. 

 As a rule, the droj) falls without a horizontal component, so that the rim 



