ScHAW. — Australasian Weather-charts and N.Z. Storms. 69 



by cyclones it generally is rapidly diminished in extent and 

 pressure, and the lows advance towards each other ; but if 

 this advance of the lows be across Australia they soon shallow 

 and die out — as I conceive, because their inherent force, the 

 constant condensation of vapour of water, is lost in that arid 

 land. Sometimes a large cyclone with very low pressure will 

 rapidly diminish an anti-cyclone with which it collides ; some- 

 times the regular supply to the anti-cyclone from above seems 

 to exceed the drain upon it by the cyclone, and it either is 

 undiminished or increases. 



If the high be north of the low — the most common case — 

 the effect of the outflow from the high into the low will be to 

 increase the motion eastwards of the latter, owing to the 

 eastward deflection due to the rotation of the earth. If the 

 high be east of the low the tendency will be to retard the 

 motion eastwards and to deflect the low to the south. If the 

 high be south of the low it will retard its progress ; if west 

 of the low it will accelerate its progress and deflect it north- 

 wards. These theoretical results seem to correspond generally 

 with the facts shown by the weather-charts. 



In considering the two series of Australasian weather- 

 charts which exhibit types of winter storms and summer 

 storms, we observe, first, the belt of calms and anti-cyclones to 

 extend generally farther north in winter (10° to 45°) than in 

 summer (25° to 45°), and thus to be wider in winter than in 

 summer ; secondly, that it is broken up into a series of anti- 

 cyclonic circulations, all circulating from north by west to 

 south and from south by east to north ; thirdly, that these 

 anti-cyclones seem to be mobile and pliable, yet without any 

 decided tendency to move east or west along the belt, while 

 they appear to offer great resistance to the movements of 

 cyclones.* 



The cyclones generally seem to lose their force when 

 passing over land, and to increase in force over water. They 

 have a powerful energy of motion in an easterly and northerly 

 direction, which, when unopposed, may carry them twelve 

 hundred miles in twenty- four hours; but they are often 

 checked, or even for a time forced back, by opposing anti- 

 cyclones. They rapidly alter their forms, throwing out great 

 arms of depression where the resistance is diminished by 



* It is to be noted that ordinarily, as each successive cyclonic dis- 

 turbance appears on the southwest coast of Australia, it is accompanied 

 by an anti-cyclone following it on its north-west side, which travels 

 across Australia as the cyclone progresses eastward along the south coast, 

 until the Tasman Sea is reached. Tliero a comparatively permanent anti- 

 cyclone'exists which is attacked by each successive cyclone, and with its 

 remains the following anti-cyclone blends and restores it to its normal 

 condition as the cyclone passes on eastward. 



