HYDROGRAPHY. 



During the period when the lands adjacent to these areas become 

 intensely heated, then the air of this Equatorial region is induced 

 towards them in gentle breezes, in pursuance of what we believe to 

 be the true theory. 



On the land there is no difficulty in pointing out where the highest 

 temperature exists. In some cases, however, this is more apparent 

 than in others. In none more so than in New Holland, surrounded 

 as it is by the ocean. During the period when the sun is in southern 

 declination, imparting its heat to that sterile land, the air flows towards 

 its centre from all sides. 



Travellers in the interior of New Holland are overcome with the 

 excessive heat, and make frequent mention of the long calms which 

 prevail. The rainless districts offer several other instances in which 

 the winds in like manner are concentrated ; but as some of these 

 occupy high table-lands instead of a depression, they change somewhat 

 the character and direction of the air rushing towards them in the 

 different seasons, and become quickly cooled in the absence of the 

 sun 



Wherever extended plains exist, and the surrounding country is 

 high, the cold currents of air are drawn towards these areas, — and 

 the greater the difference of temperature, the faster will be the flow. 

 In all these localities calms and sudden squalls predominate, and the 

 rain frequently falls in torrents, with great explosions of electricity. 



If the theory I wish to establish, of the circulation of the atmo- 

 sphere, be correct, we ought to find the winds pursuing their regular 

 route towards the areas of ocean and land. This is the case. The 

 ocean differs but a few degrees in temperature during the year; — the 

 land often undergoes great changes within a day. 



The great outlines of these currents on the ocean and land are given 

 on the map; and it must be apparent to all that the circulation of the 

 atmosphere cannot be reconciled with the old theory. 



It is remarkable that the effects we witness in the northern hemi- 

 sphere during the summer, do not take place in the Southern Pacific ; 

 the sun's action upon the Southeast Trade Winds contracts rather than 

 expands their limits, and causes them to veer to the northward of east, 

 even on what is supposed to be the parallel where they should blow 

 strongest, and with the most regularity. 



Instead of the summer being the fine season of the South Pacific, 

 it is the most boisterous part of the year; violent gales come from the 

 southwest and northwest. 



