286 Lieut. Maury on the Probable Belation between 



there is an increased atmospheric pressure, caused in part 

 by accumulation produced by the opposing forces of s' and S" ; 

 and in part by the downward currents. 



Having descended, s' is forced out on the equatorial side 

 of the zone and appears on the surface as A — the NE. trade 

 winds — and so continues until it reaches the belt of equa- 

 torial calms. 



Here, then, is precipitation, an ascent of atmosphere, and 

 a fall of the barometer : A now becomes S or an upper cur- 

 rent flowing in a SE. direction — i.e., from NW. towards the 

 zone of the calms of Capricorn. Here it is met by the upper 

 current from the Antarctic regions, descends with a rise in 

 the barometer again, and appears on the polar side of this 

 zone of calms, as a' — ^the prevailing NW. surface winds in 

 the extra- tropical regions of the southern hemisphere. 



A' now approaches the Antarctic regions in a spiral, 

 gyrating with the hands of a watch, and contracting its con- 

 volutions as it draws nearer and nearer the pole, where, 

 theoretically, there is another atmospherical node in which 

 a' ascends with a low barometer, and commences its return 

 towards the equator as 8' in the upper regions of the at- 

 mosphere. 



The same cause — diurnal rotation — which made the a' on 

 the surface to approach from the NW., now operates to make 

 it return as 8' in the direction whence it came. 



Arriving in the upper regions at the calm zone of Capri- 

 corn 8 meets 8' ; the two descend, and 8' continues to flow 

 in towards the equator as A', the SE. trade wind. 



Arrived at the zone of equatorial calms, it ascends, and 

 continues thence in the upper regions of the atmosphere as 8", 

 until it reaches the calm zone of Cancer. Here it descends, 

 and continues on as the SW. passage winds of the northern 

 hemisphere, whose circuit has been already described. 



Thus, at the risk of repetition and of being thought tedious, 

 I have described the progress which the wind and current 

 charts had enabled me to make in the theory of atmosphe- 

 rical circulation ; and I have presented that theory as far as 

 it had been developed in my own mind, when I received yes- 

 terday No. 1, vol. i., 4th series of the London, Edinburgh, 



