606 Sir Napier Shaw [March lo, 



Observations of the Upper Air, 



Speculation can do a good deal with the atmosphere. It goes 

 beyond the reach of our balloons, and tells us of the substitution of 

 hydrogen and the rarer gases for oxygen and nitrogen in the 

 region of the meteor and the solar electron. But from the year 

 1896 onwards there has been a systematic collection of facts about 

 the upper air by using kites to carry instruments up to heights of 

 3 kilometres or occasionally more, hallons sondes which carry instru- 

 ments up to heights of 35 kilometres — 20 miles or more — and pilot 

 balloons which give the direction and velocity of the wind at various 

 levels up to 10 kilometres, or sometimes more. 



Comparison of Fact with Speculation. 



This investigation has given us a wealth of information about 

 the upper air. The principal result is the division of the atmosphere 

 into two layers, a lower layer about 10 kilometres thick, the tropo- 

 sphere, the region of convection ; and an upper layer, the strato- 

 sphere, where there is no convection. We can use the information 

 to test some of the generally accepted ideas about cyclones and 

 anticyclones, and to compare the results of speculation with the new 

 facts. Many of the pictures which we imagined now appear to have 

 been illusions. Those of us, for example, who thought that because 

 the air was warmed from the bottom the upper part would be free 

 from sudden changes of temperature such as we get at the surface 

 were rapidly and rudely disappointed. Fig. 1 illustrates the dis- 

 illusionment. Simplicity is not apparently the characteristic of the 

 upper air. 



The Convection Theory of Cyclones and Anticyclones. 



Before giving you other examples let me quote the description 

 by which Galton introduced the name " anticyclone," because the 

 mental picture of the structure of cyclones and anticyclones, which 

 has guided the thoughts of the majority of meteorologists, has been 

 formed by the gradual elaboration of the ideas contained in that 

 description : — 



" Most meteorologists are agreed that a circumscribed area of 

 barometric depression is usually a locus of light ascending currents, 

 and therefore of an in-draught of surface winds which create a 

 retrograde whirl (in our hemisphere). 



" Consequently, we ought to admit that a similar area of baro- 

 metric elevation is usually a locus of dense descending currents, and 

 therefore of a dispersion of a cold dry atmosphere, plunging from 

 the higher regions upon the surface of the earth, which, flowing 



