SEA ROUTES, CALM BELTS, AND VARIABLE WINDS. 349 



in any other part of the Atlantic. On the edges of this remark- 

 able aerial current the wind is variable and often fitful ; the home- 

 ward-bound Indiaman resorts to and uses this stream in the atmo- 

 sphere as the European-bound American does the Gulf Stream. 

 It is shaded on the plate. 



678. These investigations, with their beautiful developments, 

 Counterpoises, cagcrlj captivatc the mind ; gi^'ing wings to the 



imagination, they teach us to regard the sandy deserts, and arid 

 plains, the moimtain ranges, and the inland basins of the earth, as 

 compensations in the gTcat system of atmospherical circulation. 

 Like counterpoises to the telescope, which the ignorant regard as 

 incumbrances to the instrument, these wastes serve as make-weights, 

 to give certainty and smoothness of motion — facility and accuracy 

 to the workmgs of the machine. 



679. When we travel out upon the ocean, and get beyond the 

 Normal state of the influeuce of the land upon the ^inds, we find our- 

 atmosphere. sclvcs in a field particularly favourable for studying 

 the general laws of atmospherical cnculation. Here, beyond the 

 reach of the great equatorial and polar currents of the sea, there are 

 no unduly heated surfaces, no mountain ranges, or other obstruc- 

 tions to the chculation of the atmosphere — nothmg to disturb it 

 in its normal coui'ses. The sea, therefore, is the field for ob- 

 serving the operations of the general laws which govern the 

 movements of the great aerial ocean. Observations on the land 

 will enable us to discover the exceptions, but from the sea we 

 shall get the rule. Each valley, every mountaui range and local 

 district, may be said to have its own peculiar system of calms, 

 winds, rains, and droughts. But not so the surface of the broaa 

 ocean ; over it the agents which are at work are of a more uiuform 

 character. 



680. PiAiN-^vMiNDS are the winds which convey the vapour from 

 Eain--nir.ds. the sca, whcrc it is taken up, to other parts of the 



earth, where it is let do^n either as snow, hail, or rain. As a 

 general rule, the trade-T\dnds (§ 293) may be regarded as the 

 evaporating miids ; and when, in the course of their chcuit, they 

 are converted iuto monsoons, or the variables of either hemisphere, 

 they then generally become also the rain-^wds — especially the 

 monsoons — for certain localities. Thus the south-west monsoons 

 of the Indian Ocean are the rain winds for the west coast of Hin- 

 dostan (§ 298). In like manner, the African monsoons of the 

 Atlantic are the winds which feed the springs of the Niger and the 



