332 



registered from 1 to 2 inches, while on parts of the Mount 

 Lofty Ranges the totals exceeded 3 inches, with a maximum 

 of 534 points at Uraidla. 



"The passage of a low-pressure trough usually coincides 

 with the maximum of atmospheric instability, and in this 

 case it seems probable that the exceptional energy developed 

 was in some way connected with the arrival of the colder 

 and denser air of the anticyclonic front, for the sudden 

 change from cyclonic to anticyclonic conditions is almost 

 invariably associated with violent atmospheric disturbances, 

 and not infrequently thunder and hailstorms. Winter 

 thunderstorms are by no means uncommon over the southern 

 parts of Australia ; in fact, they are nearly always asso- 

 ciated with deep antarctic disturbances. As the centres of 

 these systems, however, chiefly keep well over the ocean, the 

 full effect of the storms is seldom felt on the mainland." 



"E. Bromley, 

 "Divisional Officer, Weather Bureau, Adelaide." 



DESCRIPTION OF PLATE XVI. 



(All figures are of natural size.) 



Fig. 1. Spherical form, shoAving radial and concentric lines 

 in clear ice. Hailstones of this type fell at the beginning of the 

 storm, and, later, formed the nucleus of larger ones, as seen in 

 figs. 2, 3, 4, 5, 6. 



Fig. 2. Lenticular hailstone, showing nucleus surrounded by 

 a corona of small ice fractures Avith beads or blunt prominences 

 on the peripheral margin. A. — Side view; B. — Shows lenticular 

 outline. 



Fig. 3. Subspherical hailstone with a protuberance on one 

 side, giving it a flask-shaped outline. 



Fig. 4. Oblong and subquadrate hailstone with tAvo pro- 

 tuberances symmetrically arranged. 



Fig. 5. Lenticular hailstone with short spines on the peri- 

 pheial margin. 



Fig. 6. Lenticular hailstone, with a sharply-pointed spine 

 three-quarters of an inch in length, and the bases of three other 

 spines in positions antipodal to each other, in pairs. 



Fig. 7. Agglutinated compound hailstone, OA T ately-spherical 

 in outline, consisting, apparently, of a group of hailstones that 

 had coalesced and Avere united by relegation films that had the 

 appearance of septal bands between the respective units. Tavo of 

 these stood out prominently and formed knobs at the extremities 

 of the longer axis. 



Fig. 8. A compound hailstone, in which four units were 

 symmetrically combined in a subglobular cruciform pattern. Taao 

 small spines, of uniform size and outline, extended from each 

 extremity of the longer diameter. This hailstone fell during a 

 storm in Adelaide on July 3, 1917. 



