SOME WORLD'S WEATHER PROBLEMS 211 



Now what does the presence of this see-saw inform us? 



The reader must in the first instance be reminded that the 

 amount of atmosphere surrounding our globe may be regarded 

 as an invariable or constant quantity. The reduction of it, 

 therefore, in any one part of the world must be counterbalanced 

 simultaneously by a corresponding increase in another region. 

 Now this large barometric see-saw tells us that such a 

 transference of air is really in operation, and the direction of 

 this exchange is from east to west and from west to east 

 alternately, and not between the equatorial and polar regions. 



160 ISO 120 80 40 



40 80 120 



160 E 



Fig. 1. 

 Map to show the central areas and boundaries (thick lines) of the two extensive regions the 

 pressures over which behave in a see-saw manner. Previously known see-saws for 

 special areas are joined by continuous straight lines. 



It is difficult at the present time to give even an approximate 

 idea of the amount of air that is being moved backwards and 

 forwards ; but the quantity must be very considerable, since it 

 can so easily be detected by the changes of the barometer. In 

 the first instance it was thought that possibly we might here 

 be in the presence of a wave of high and low pressure travelling 

 round the world ; but further investigation showed that this 

 was not the case, but that simply a huge to-and-fro action, 

 world-wide in extent, was occurring. The reader may next 



