1904.] Short-Period Atmospheric Pressure Variation. 469 



which it is very difficult to say exactly which type is followed, and 

 as he says there may be " differences of opinion as to the assignment 

 of some of these curves, but the reader can make any different 

 arrangement that he prefers." 



In most of the main features, however, his map suggests a somewhat 

 similar distribution of these pressure types to that given here. Thus, 

 he finds that "the region around the Indian Ocean gives direct 

 synchronism, South America and North America give inverse 

 synchronism, while Europe and Siberia give an indifferent type. 

 Greenland and Iceland seem to have direct type like the Indian 

 Ocean .... 



" The eastern hemisphere tends to direct synchronism, except in 

 Europe and Eussia where the indifferent type prevails, and the 

 western hemisphere to the inverse type." 



It may be further pointed out that regions which are the reverse of 

 one another as regards these secular pressure variations should very 

 probably experience opposite kinds of abnormal weather, while those 

 over which the same type of pressure variation exists should have 

 weather of an abnormal but similar nature. 



That this is inclined to be so as regards the latter statement has 

 been recently* very forcibly pointed out by Sir John Eliot with 

 respect to the Indian area. He writes : — 



"The drought of 1895 — 1902 was a more or less general meteoro- 

 logical feature of the whole area, including Abyssinia, East and South 

 Africa, Afghanistan, India, probably Tibet, and the greater part or 

 whole of Australia." 



The whole of this region, as will be seen from the accompanying map 

 (fig. 1), is embraced by the ( + ) type of pressure. 



In the light, therefore, of the existence of these large regions of 

 opposite pressure types, it is vital in the interest of long-period fore- 

 casting that observations from all portions of the globe should be 

 included in any discussion. 



Several years ago Eliotf drew attention to these oscillations of 

 pressure of long period, other than the diurnal and annual oscillations 

 in India. In this important memoir he pointed out that " they are 

 directly related to the largest and most important features of the 

 weather in India, viz., the character and distribution of the precipita- 

 tion of rain and snow in the Indian monsoon area." 



There is reason, therefore, to believe that this short period pressure 

 variation will in the future be of considerable assistance in helping 



* ' Broad "Views,' p. 193 ; ' The Meteorology of the Empire durirsg the Unique 

 Period 1892—1902,' by Sir John Eliot, K.C.I.E., F.R.S. 



f " A Preliminary Discussion of certain Oscillatory Changes of Pressure of Long 

 Period and of Short Period in India," ' Indian Met. Memoirs,' vol. 6, part 2, 1895. 



