170 



Meteorology of Melbourne. 



p.nd resistance to tlie wind which occurs at the earth's surface, 

 than in the upper and free regions of the atmosphere. From 

 the influence of this cause it is easy to understand that the upper 

 current of air would retain its velocity or momentum in its 

 progress to the poles^ so as to be enabled at a certain distance 

 from the tropics to overcome the more sluggish lower current^ 

 and force it into its own direction. It is evident that the 

 cuiTcnt of air towards the poles can only be equal to that 

 which is flowing towards the equator ; I suppose^ therefore^ 

 that in the belt in which the westerly winds prevail^ the upper 

 current has overcome the lower, only by communicating its 

 own westerly and not its southerly direction. 



With I'cspect to the winds of Australia it is to be observed 

 that we have a very large island or continent, of a compact 

 form, not deviating greatly from that of a circle, and for the 

 most part remote from any other large tract of land. Of this 

 immense region a part is situated within the tropics, and the 

 remainder very close outside the tropics, so that, having much 

 higher temperature than that of the surrounding ocean, the land 

 may be considered as a vast heating surface, which, on the prin- 

 ciples already explained, will have a tendency to draw currents 

 of air in all directions towards its centre of heat. There can 

 be no doubt that the hottest part of the island exists to the 

 northward, and probably also to the westward of the geogra- 

 phical centre. The influence of the trade winds within the 

 tropics would probably throw this point towards the west ; 

 and, in confirmation of this view, I would observe that the 

 hottest part of the ocean in the vicinity is south of the line, 

 and to the N. W. of Austraha, according to Black's map of 

 Physical Geography : — viz. Java and Timor. For the sake 

 of illustration, we will suppose the hottest point to be in 

 long. 130^ and lat. 22^ or a little to the N. W*. of Sturt's 

 Desert. Confining our investigations to the southern portions 

 of the continent, we have next to consider that the wind, 

 blowing outside the coast, has a prevailing direction from 

 west to east, and therefore on approaching the coast it would 

 not at once assume a direction towards the centre of heat, but 

 rather a direction intermediate between that and its original 

 eastward motion. 



On proceeding along the line of coast from west to east, we 

 fehall expect, on this principle, to find the westerly character of 

 the wind gradually diminished, and that It will at a certampomt 

 become southerly, and beyond that again more or less easterly. 

 Thus in South Australia the prevailing winds ought to be 



