AN ESSAY ON SOUTHERLY BURSTERS. 175 



<;omes out one thousand eight hundred and thirty feet, and it 

 spread over at least 100° of the horizon, seventy of which the 

 photograph includes. The sun had set at 6-38 p.m., and night 

 was closing in fast, hastened by the dark masses of cloud which 

 almost covered the sky. 



At 6*45 p.m., a long way off and due south, a thunder squall 

 was seen and no doubt marked the arrival of the burster there, 

 showing that the axis of the \ was still inclined to south-south- 

 east as it was in the morning. The rate of motion of the axis of 

 the y\ eastward to Sydney from its barometrically denned position 

 at 9 a.m., three hundred miles west of Sydney, to the Observatory 

 by 7 p.m. i.e., in ten hours, is seven hundred and twenty miles 

 per day, and agrees fairly well with the rate of the whole system 

 from map 5 to map 6, that is eight hundred miles in the twenty- 

 four hours, or thirty-three miles per hour. 



In the original photograph delicate shading shows the rounded 

 oloud perfectly, with another delicate roll above it, but much of 

 the fine detail is lost in the reproduction. 



DANDENONG GALE. 



I have also added a diagram, (page 153) giving barometer and 

 anemometer conditions at Sydney during the famous Dandenong 

 gale, for comparison, the extensive and disastrous possibilities which 

 a burster may develop made this desirable. During this gale 

 the wind attained, locally, to the abnormal velocity of one hundred 

 and fifty-three miles per hour in a gust, the rate of one hundred 

 and twelve miles for ten minutes, and fifty-seven miles per hour 

 for nine hours, while its influence was severely felt for hundreds 

 of miles in every direction. The most remarkable points in this 

 diagram are, first the comparatively steady barometer curve ; and 

 second, the pulsatory action of the wind velocity shown by the 

 mean hourly number of miles registered during the heaviest part 

 of the gale. 



UNFAVOURABLE SEASONS FOR CLOUD OBSERVATIONS. 



The opportunities for making cloud observations this summer 

 have been eminently unfavourable, but I have made the best 



