22 Mr. E. M. Deeley on the 



There is thus a very marked difference between the two hemi- 

 spheres. In the more land-covered hemisphere the tempe- 

 rature differences are greater between summer and winter 

 than they are in the more water-covered hemisphere. 



If the winds are due to temperature differences, then they 

 should likewise show marked differences in the two hemi- 

 spheres. In the Southern Hemisphere the temperature 

 gradients from north to south are fairly regular along all 

 meridians ; whereas in the Northern Hemisphere the tempe- 

 rature gradients along meridians passing over the continents 

 differ widely from those passing over the oceans. 



In figs. 6 and 7 the arrow-heads on the curves show the 

 north or south components of the prevalent winds. It will 

 be noticed that on the two meridians, both in June and July, 

 at higher latitudes than 30° in the Southern Hemisphere, the 

 winds blow against the surface temperature gradients. A 

 similar state of affairs exists in the Northern Hemisphere 

 during January; but in July along the meridian 75° E. 

 the wind blows in accordance with the surface temperature 

 gradient. In the equatorial regions between 30° S. lat» 

 and 30° N. lat. the winds everywhere follow the temperature 

 gradients. We see from this that in middle latitudes the 

 winds do not always obey Halley's surface temperature 

 gradient theory, but that in the equatorial regions they do. 



An inspection of a chart showing the mean directions of 

 the winds for each month, will make it clear that figs. 6 and 7 

 represent with fair accuracy the general relationship between 

 the direction of flow of the winds and the surface temperature 

 gradients. 



When dealing with the effects of the rotation of the earth 

 on the paths of the winds, it was pointed out that when the 

 air circulates round cyclonic centres it is compressed on one 

 side and expanded on the other, so as to produce pressure 

 variations on the earth's surface. These differences of 

 pressure are registered by the barometer. By drawing lines 

 of equal mean pressures on a map, and then comparing the 

 map so produced with a map showing the directions followed 

 by the winds for the same period, a very close agreement 

 will be found to exist between the areas of low pressure and 

 the cyclonic winds and between the areas of high pressure 

 and anticyclonic winds. Indeed, as has already been stated, 

 a very close relationship exists between the directions and 

 force of the winds and the trend and steepness of the baro- 

 metric gradients. It must be remembered that we are 

 dealing with the prevalent surface winds and the mean baro- 

 metric gradients, for these show the nature of the genera 



