I905-] CONDITIONS OF THE TRADES-MONSOON AREA. 161 



perience of the Indian area will be found to correspond with that 

 of the United States. It must however be born in mind that the 

 investigation is one of extreme complexity and that superposed on 

 the four-year or minor oscillation there are great irregularities 

 which cannot now be explained but which at times completely upset 

 the regular course of the cycle. Notwithstanding these irregulari- 

 ties and interruptions it appeared to the writer that in face of the 

 remarkable agreement between the pressure oscillations and the 

 rainfall during the years 1893 to 1899 ' li was worthwhile to con- 

 tinue the discussion in a more exact and detailed manner so as to 

 determine (1) over what area the pressure oscillations extended 

 (2) how far they agreed in amplitude and in time throughout the 

 affected area and (3) what relation the rainfall of the whole mon- 

 soon area bore to the pressure oscillations. 



The author has collected and discussed a large amount of ma- 

 terial and has arrived at certain conclusions which he regards as 

 tentative and far from satisfying. He feels doubtful if the obser- 

 vations would fulfil the requirements which Professor Schuster laid 

 down as a means of estimating the reality of the periodicity, but the 

 investigation has brought out certain relationships which appear at 

 least worthy of record. 



The tentative conclusions arrived at are as follows : 

 (1) That over the trades monsoon area — and most markedly 

 so over the equatorial belt — there occur four-year oscillations of 

 pressure; (2) that during the rising portions of these oscillations 

 the general rainfall of the trades monsoon area is below, and dur- 

 ing the falling portions is above the average, with a well-marked 

 minimum of rainfall in the first year of the cycle and a well-marked 

 maximum of rainfall in the third year ; (3) that from the Antarctic 

 or extreme southern regions there emanate at irregular intervals 

 rays or streamers of varying extent and intensity which occasion 

 increased atmospheric pressure over the affected area; (4) these 

 rays or streamers are apparently not in the least in the nature of 

 waves, as they affect large areas practically simultaneously and con- 

 tinue for considerable periods; (5) when these rays or streamers 

 are frequent and extensive, as in portions of the years 1899 and 

 1900, pressure ranges largely above the normal, but exhibits large 

 oscillations or fluctuations ; when on the contrary they are absent 

 as in portions of the years 1898-1899 pressure is low and the oscil- 



