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NOTES ON THE REMARKABLE HAILSTORM NEAR 

 ADELAIDE, ON MAY 12, 1917. 



By Walter Howchin, F.G.S., Lecturer in Geology, 

 University of Adelaide. 



[Read July 12, 1917.] 

 Plate XVI. 



A thunderstorm passed over the southern suburbs of 

 Adelaide on the morning of Saturday, May 12, 1917, and 

 was accompanied by hailstones of unusual size and of peculiar 

 forms. Tiiere had been mutterings of distant thunder with 

 showers during the preceding night. Between 9 o'clock and 

 10 o'clock on the morning of the 12th a densely-black cloud 

 appeared to the north-west, showing violent agitation along 

 the advancing front of the storm. As the cloud overspread 

 the sky thunder was heard and rain began to fall. Several 

 flashes of lightning and thunder-claps occurred in quick suc- 

 cession, and were followed by a deluge of rain, accompanied 

 by hailstones. The fall of hail was in two sections, separated 

 by an interval of only a few minutes, during which the rain 

 nearly ceased, and only sporadic hailstones, mostly of large 

 size, fell ; the second of the maxima being of the greater 

 intensity, and was accompanied by the largest hailstones. 



The Hailstones. 



The common type of hailstone, which is soft, white, and 

 snow-like, was apparently absent, or, if present, was obscured 

 by the more numerous and larger examples. So far as my 

 observation went the hailstones that fell in the shower were 

 of the hard kind, and consisted almost entirely of clear and 

 transparent ice. One notable feature was a great uniformity 

 of form under several well-marked types. Among the more 

 distinctive of these were the following : — 



1. Smooth Spherical Forms (pi. xvi., fig. 1). — These 

 were perfectly round and smooth, of a dull white colour, and 

 of all sizes up to about five-eighths of an inch in diameter, 

 or a little more than that. Up to this size they were as 

 round as marbles (which they greatly resembled), and in 

 colour and smoothness were similar to the nitre-balls sold 

 by chemists. Some of the same type reached a size of three- 

 quarters of an inch, but the larger examples were not quite 

 so symmetrical as the smaller ones. Many of these hard, 

 spherical forms, on striking the ground, split in halves, like 

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