40 AUSTRALIAN WEATHER. 



From this table it will be seen that the wind changed to south 

 at Eden, the southern point of the coast at 2 a.m., and made its 

 way gradually up the coast, reaching Sydney at 1 p.m. and New- 

 castle at 3 g 40 p.m. in the mean time that is at 2 p.m. Port 

 Macquarie, one hundred and ten miles north of Newcastle, reports 

 the change at 2 p.m., or one hour and forty minutes before it got 

 to Newcastle, or to put it another way, when one burster reached 

 a point on the coast twenty miles north of Sydney, another made 

 itself felt at Port Macquarie, one hundred and ten miles farther 

 north, it appears then that there were two bursters separated by 

 one hundred and ninety miles and simultaneously making their 

 way along the coast. It is probable, however, that the southerly 

 burster is a line storm, and that the change of wind occurs along 

 a certain isobar, and if this be the true explanation it is entirely 

 in accordance with what has already (page 29) been shown as to 

 the trend of the isobars in certain cases. When the approaching 

 anticyclone flattens its isobars against our dividing range, and 

 then taking advantage of the easier western slope in the northern 

 districts, and the lower altitude of the mountains generally, to 

 the west of Port Macquarie, protrudes some of the isobars over 

 the mountains, so that they come to the eastward at that point 

 like a nose or easterly extension of the isobars, while the southern 

 half of the anti-cyclone is retarded. This feature was noticeable 

 upon the occasion in question, and, as is invariably the case under 

 such circumstances, thunderstorms were prevalent. These, I think, 

 may be safely accepted as the causes which give rise to the 

 phenomenon of two simultaneous, yet entirely independent, 

 bursters. 



In speaking of the areas over which the burster exercises its 

 coastal influence, mention has been made of the fact that it is rarely 

 met with north of Port Macquarie. The present case was not, 

 in reality, any exception to the general rule ; the burster did not 

 reach Clarence Heads as such, and the change there was simply a 

 veering of the wind from north-east through west to south-east, 

 accompanied by a thunderstorm and hail. The downfall of hail 



