DISCUSSION AND ANALYSIS OP WINDS, 665 



branch of the Murray River, 30.217. Hence a higher pressure occurs at this 

 season (winter) in the interior, and it may be inferred that it is greatest in the 

 southern portion of the interior. The prevaihng winds are these : At Brisbane, 

 S. S. W. ; Sydney, W. by N. W. ; Melbourne, N. ; Adelaide, N. E. by N. ; Free- 

 mantle, N. E. by E. ; in other words, the winds blow out from this space of high 

 pressure." 



"This behavior of the winds with respect to spaces of high pressure differs in no 

 respect from what occurs on particular days on which the isobaric lines present 

 the same conditions of pressure. Mr. Francis Galton first drew attention to this 

 peculiarity, under the name of Anticyclones, by which name he intended to convey 

 the idea that in cases of high pressure occurring over a limited area, the course of 

 the winds is exactly the reverse of what is seen to prevail in cyclones in which the 

 winds blow round and in upon a space of low pressure." 



" The ouffloio of tire air from a region of high pressure, and the infloio upon a 

 region of low pressure, appear to be reducible to a single principle, viz., the princi- 

 ple of gravitation. Given as observed facts the differences of pressure, it might 

 almost be predicted, before calculating the averages, what the prevailing winds are. 

 Indeed, so predominating is the influence of gravitation, that it may be regarded 

 as the sole force immediately concerned in determining the movements of the 

 atmosphere. If there be any other force or forces which set the winds in motion, 

 their influence must be altogether insignificant as compared with gravitation." 

 (Buchan, p. 581 to 583.) 



This last passage of Buchan may be more distinctly expressed : in the action of 

 gravity in restoring the equilibrium disturbed by unequal temperature. With a 

 uniform temperature over the whole earth, there would be no wind. In illustra- 

 tion of the dependence of the wind on the difference of pressure, the map of 

 isobars, Plate 14, as well as Plates 2, 4, 5, 6, and others, should be consulted. 



Having given the above examples of the manner in which the winds are affected 

 by atmospheric pressure, it is necessary to account for the origin of areas of high 

 pressure, out of which, it is seen, the winds flow. 



It must be said that this question is one of the most difficult in meteorology, 

 and far from having received an entire solution. 



As the tropical regions present the meteorological phenomena in the simplest 

 form, it is best to begin with them. It has been known for a long time, that above 

 the lower current of the air of the trade winds, flowing in the lower latitudes of 

 the northern hemisphere from N. E. or E. N. E., there exists an upper one from 

 about W. S. W. The existence of this current was proved by the movement of 

 the highest (cirri) clouds always from some westward point, from the strong west- 

 erly winds on high mountains in the trade-wind region (the Chimborazo and others 

 in equatorial South America, the peak of Teneriffe, etc.), from the transport east- 

 ward of ashes from the eruption of the volcanoes on the island of St. Vincent, 

 (West Indies), and Cosiguina (Central America), and also from the direction of 

 the smoke of very high volcanoes of the tropics. The suppositioyii was then made, 

 that there was a powerful ascending current over the belt of calms and rains near 

 the equator, and that the air thus ascended flowed in the upper regions of the 



84 July, 1875. 



