THE WINDS. 289 



Upon the limits of the permanent monsoon, the place for the calms 

 remains for the night, to be turned back to the land and to the 

 hills the following day by the sea-wind. In evely place where 

 these calms go, the land and sea winds turn back. If various ob- 

 servers, placed between the hills and the sea, and between the coast 

 and the farthest limit of the land-wind, noted the moment when 

 they perceived the calms, and that when they perceived the land- 

 wind, then by this means they would learn how broad the belt of 

 calms has been, and with what rapidity they are pushed over the 

 sea and over the land. And even though the results one day 

 should be found not to agree very well with those of another, they 

 would at least obtain an average thereof which would be of value. 

 So, on a larger scale, the belt of calms which separates the mon- 

 soons from each other, presses in the spring from the south to the 

 north, and in the fall from the north to the south, and changes 

 the monsoons in every place where it presses."* 



835. The Calm Belts. — There is between the two systems of 

 trade-winds a region of calms, known as the equatorial calms. It 

 has a mean average breadth of about six degrees of latitude. In 

 this region, the air which is brought to the equator by the north- 

 east and southeast trades ascends. This belt of calms always 

 separates these two trade-wind zones, and travels up and down 

 with them. If we liken this belt of equatorial calms to an im- 

 mense atmospherical trough, extending, as it does, entirely around 

 the earth, and if we liken the northeast and southeast trade-winds 

 to two streams discharging themselves into it, we shall see that 

 we have two currents perpetually running in at the bottom, and 

 that, therefore, we must have as much air as the two currents 

 bring in at the bottom to flow out at the top. What flows out 

 at the top is carried back north and south by these upper currents, 

 which are thus proved to exist and to flow counter to the trade- 

 winds. 



836. Using still farther this mode of illustration : if we liken 

 the calm belt of Cancer and the calm belt of Capricorn each to a 

 great atmospherical trough extending around the earth also, we 



* Bijdrage Natuurkundige Beschrijving der zeen, vertaald door M. H. Jansen, Lui- 

 tenant ter zee. 



