Meteorology of Melbourne. 



173 



ing of independent currents of air, the winds have a tendency 

 to blow in curves, both horizontal and vertical, rather than in 

 straight lines. 



When a hot wind blows out to sea, it is cooled by contact 

 with the water ; but, at the same time, in consequence of its 

 elevated temperature, it induces rapid evaporation, and 

 becomes loaded Avith moisture. In propoi^ion to the fall^ of 

 the barometer, indicating the greatness of the vacuum which 

 originally caused the descent of the hot wind, and the deposi- 

 tion of moisture occurring at the line of its meeting with the 

 southerly wind, will be the tendency of the southerly and 

 westerly winds eventually to become set in motion, in order 

 to restore the equilibrium. The meeting of the cold with the 

 hot wind, both comparatively loaded with moistiu-e, will cause 

 an immediate deposit in the form of clouds and rain. We 

 have in fact the hot wind blown back upon ns, ^after having 

 been to sea, as it were, to bring back water. 



We are apt to complain of these hot winds as one of the 

 principal inconveniences of the climate. Had we however no 

 hot winds, we should probably have little or no rain. The 

 southerly winds would not bring it, because as they proceed 

 northward they become warmer and drier^ and have less and 

 less tendency to deposit their moisture. Even the winter 

 rains are usually the consequence of a northerly, although we 

 do not at that season call it a hot wind. 



The great redeeming feature of the Australian hot wind, is 

 its low dew-point, or in other words, its dryness ; but for this 

 it would be intolerable. It is easy to conceive that with the 

 thermometer at 112^ and the air nearly saturated with 

 moisture, profuse perspiration would be caused, but it would 

 not be removed from the surface of the body, and the effect on 

 the system would be nearly the same as if it were immersed 

 in a scalding hot bath. It were vain to hope, and wrong to 

 wish, that the hot winds of Australia should ever be abolished. 

 But much uiay be done in the next generation to mitigate 

 their Inconvenience. The cultivation of the land, and especially 

 the extensive planting of trees, will have some influence. 

 The leaves of trees and shrubs act almost as wet cloths 

 suspended in the air, and the cooling effect of evaporation from 

 their surface is very considerable ; added to which, is the 

 probable cold produced by the absorption of carbon, by which 

 an effect, the reverse of that produced by its oxidation or 

 combustion, may be produced. The coolness of ripening 

 fruits may perhaps be accounted for on this principle. The 

 construction of houses, whether in adaptation to the exigencies 



