Turning of the Wind. 103 



recent researches and discoveries in this branch of science 

 have illustrated the value of what we have gained and what 

 we still hope to gain. 



Before entering into the enumeration of facts which tend 

 to support Dove's " Law of Turning/' it will he perhaps well, 

 in order to prevent misunderstanding, to give in short outline 

 the principles of this law, although I am quite aware that 

 many of the members are quite conversant with them. 



First of all, it must be understood that the southern coast 

 of the Australian continent, from a geographical-meteorolo- 

 gical point of view, is situated in the ec-tropical region of our 

 globe, which is justly called the central system, or the region 

 of the oblique alternating winds. 



The continuous effect of the sun's heat gives rise to an as- 

 cending current of air within the tropical region (current 

 ascendant) which, after having reached a great elevation, 

 flows off towards the poles, the direction of the current being 

 consequently in the southern hemisphere south, and in the 

 northern hemisphere north, if we suppose our globe to have 

 no rotation round its axis. The cold air from the polar 

 regions rushes into the rarified space thus produced, which 

 manifests itself by a current of air towards the north or the 

 south, as we may suppose ourselves to be in the southern or 

 northern hemisphere. These two currents pursue their 

 courses above each other until the upper one of warm air 

 descends into the lower regions of our atmosphere, and then 

 makes its way on the surface of our globe. The latitude in 

 which this takes place varies greatly throughout the year, 

 following the declination of the sun, and is on an average 30 

 degrees at both sides of the equator.* Within those two 

 parallels we have the intertropical, or, as some savans call it, 

 the peripherical system of winds, and beyond them we have 

 extending in both hemispheres towards the poles the central 

 system, with its equatorial limit bounded by the subtropical 

 belt, within the area of which falls the point of contact of 

 the descending compensating wind varying throughout the 

 year. The breadth of this latter girth is consequently given 

 by the amplitude of the oscillations of the point of contact 

 of the descending current. As soon as the compensating 

 wind has reached the surface of the globe, it meets the 

 current coming from the poles, and the relations between 



* The limits of the region of the trade winds depends greatly upon the 

 configuration of the continents. 



