SOUTHERLY BURSTERS. 31 



active high pressure in the rear at the commencement of the blow. 

 The gale of 1892 was not a burster, but a gradual change to south 

 which took place some thirty hours previously. In this instance 

 the A depression, which seemed to act in concert with the 

 tropical cyclone, appears to have backed from a situation midway 

 between Australia and New Zealand. 



CONDITIONS WHICH REGULATE THE NUMBER OF BURSTERS. 



Before proceeding further, ib may be advisable to offer a sug- 

 gestion as to the causes which seem to the writer to justify the 

 two apparently anomalous statements made in an earlier part of 

 this essay : (1) that bursters are less frequent and also less violent 

 than usual, during those seasons when the interior of the country 

 is suffering from drought ; and (2) that they are also less frequent 

 and of less than their ordinary violence, when the same region is 

 visited by persistent rains with overcast skies. In other words, 

 seasons of drought and desolation and seasons of deluge are both 

 inimical to the existence of bursters. 



The following theory is tentatively submitted, to account for 

 the greater prevalence of bursters during what may be called a 

 moderately dry season. This term is used here to indicate, not 

 so much a season in which the rainfall does not exceed the 

 average, as one in which the number of rainy days is a shade 

 below the average. It will be remembered that strong southerlies 

 have been said to result from energetic anticyclones ; also that 

 energetic anticyclones bring with them possibilities of great 

 extremes in our summer temperatures. But since in summer 

 their sphere of action is in high latitudes the weather of the 

 northern parts of Australia is controlled chiefly by tropical 

 depressions, and consequently great heat prevails there as a rule. 

 Now if, after a period of hot weather, rain were suddenly pre- 

 cipitated on this northern area, the consequence would be a great 

 uprush of air with the vapour produced by the rain falling on 

 heated ground, and a consequent inrush of air from southern 

 areas. 



