452 R. M. Deeley — Polar Climates. 



blow is of the utmost consequence. But it cannot be said that there 

 is any general agreement among meteorologists as to the reasons why 

 the general winds of the earth blow in the directions they do. If the 

 flow were due to the temperature gradients as they now exist on the 

 earth's surface, then the cold air at the Poles should flow towards 

 the Equator as north-easterly winds in the Northern, and as south- 

 easterly winds in the Southern Hemisphere, and there should be 

 currents in the higher atmosphere moving towards the Poles. We 

 should then have a belt of lowest pressure in Equatorial regions, and 

 two high-pressure areas, one over the North Pole and another over 

 the South Pole. 



But the prevalent winds do not uniformly blow as above indicated. 

 There is the low-pressure belt, and the winds as above described, in 

 Equatorial regions ; but instead of these winds coming from the Polar 

 regions they come from two fairly continuous high-pressure belts at 

 latitudes 30° north and south of the Equator. 



In higher latitudes in the Northern Hemisphere the winds generally 

 flow polewards as south-westerly winds at the earth's surface and 

 north-westerly winds in the higher atmosphere. These are, of course, 

 the general winds. In many continental areas, such as the Asiatic 

 one, the change of temperature with change of season is very great, 

 and we get such winds as the monsoons, which do not blow as do the 

 trade winds or the prevalent winds of middle latitudes. In the 

 Southern Hemisphere the north-west winds of middle latitudes blow 

 much more regularly than do the south-west winds of the Northern 

 Hemisphere. 



Many theories have been propounded to account for these apparently 

 anomalous winds of middle latitudes ; but not one of these theories 

 has received anything like general support, for they all fail in some 

 respects to account for the facts. That a correct explanation of the 

 circulation of the atmosphere should be found is most important from 

 a climatological point of view, for such a theory may enable us to 

 predict what effects would be produced if certain geographical changes 

 occurred. 



I have lately attempted to base a theory * upon the contentions of 

 Halley and Hadley ; but instead of considering the winds as blowing 

 in accordance with the surface temperature gradients, they are 

 regarded as being due to the horizontal temperature gradients of the 

 whole thickness of the atmosphere. Kecent soundings by registering 

 balloons for ascertaining the temperature of the atmosphere have 

 shown that the temperature of the upper atmosphere is greater in 

 high latitudes than it is over the Equatorial regions. This is a very 

 surprising fact, and if the temperature gradient of the upper atmo- 

 sphere should be proved by further observation to be as great generally 

 as the many hundred soundings already made show, then the upper 

 temperature gradient should overpower the lower temperature gradient 

 in middle latitudes and cause the lower winds of middle latitudes to 

 move towards the Poles. 



It is now recognized that the atmosphere may be divided into two 



1 Phil. Mag., July, 1915, pp. 13-33. 



