210 SCIENCE PROGRESS 



pressure between Siberia and Indo-Malaysia and Australia. 

 In other words, when in some years the pressure in Siberia 

 was extra high, that in Indo-Malaysia and Australia was cor- 

 respondingly low. More recently the great Swedish meteoro- 

 logist Hildebrandsson discovered that there were several 

 regions which behaved in this see-saw manner with each 

 other, and such localities he termed " centres of action " of 

 the atmosphere. Thus the Azores and Iceland behaved in 

 this manner, and also Siberia and Alaska, Tahiti and Tierra 

 del Fuego, India and Siberia, Greenland and Key West, and 

 Buenos Ayres and Sydney (Australia). 



The present writer, with Sir Norman Lockyer, carried the 

 investigation still further forward, and examined the pressure 

 changes at ninety-five stations scattered all over the globe. The 

 result of this inquiry led to the discovery that there really 

 existed only one large see-saw, and this between nearly antipodal 

 parts of the earth ! In fact, it seemed that the Indian region 

 was about the centre of one area, while the Argentine and 

 Chili formed the centre of the antipodal region. By classifying 

 the different types of pressure changes according as they re- 

 sembled the two main and opposite types, namely, Bombay 

 (India) and Cordoba (Argentine), it became possible to trace 

 out a boundary line separating these two large areas. It was 

 at once seen that each of the regions which Blanford and 

 Hildebrandsson had pointed out as behaving in a reverse 

 manner to each other were situated on opposite sides of this 

 boundary line, and should therefore exhibit opposite pressure 

 changes, according to the nature of this large see-saw. A 

 similar classification of pressure types was undertaken by 

 Professor Bigelow, of the United States Weather Bureau, and 

 he corroborated almost exactly this world-wide barometric 

 surge. 



The accompanying map (fig. i) shows the world divided 

 into these two large regions. The continuous and dotted curved 

 lines represent iso-phase conditions in the eastern and western 

 hemispheres respectively, and the boundary between them is 

 shown by the heavy lines. The see-saw regions referred to by 

 Blanford and Hildebrandsson are connected by straight lines, 

 which, as will be seen, all, with one exception — namely, that 

 between Tahiti and Tierra del Fuego, which has been here 

 omitted — cross the boundary line. 



