586 MR ALEX. BUCHAN ON THE MEAN PRESSURE OF THE ATMOSPHERE 



Thus the number of stations, at which the greater maximum direction of the 

 wind is S.W., and the smaller, N.E., is 15. Further, if the whole 115 stations be 

 examined, and those picked out at which the greater maximum direction is from 

 any point between S.S.W. and W., and the smaller maximum from any point 

 between N.N.E. and E., the number is found to amount only to 34, or less than 

 30 per cent, of the whole. Now, since these are the directions in which truly 

 equatorial and truly polar atmospheric currents should blow, it is evident that 

 these two currents, as often represented, are not the two prevailing winds 

 generally observed over the north temperate zone. For if the two great 

 currents of the atmosphere were, one flowing from subtropical regions towards 

 the poles, and the other flowing from the poles towards the tropics, it is plain 

 that a much larger percentage of the stations than 30 would follow the course of 

 these currents in the north temperate zone. If to these 34 stations, at which the 

 maximum directions are in the course of the equatorial and polar currents 

 respectively, we add 17 stations, at which the greater maximum direction is from 

 N.N.E. to E., and the smaller from S.S.W. to W., the number of stations at 

 which the two prevailing winds follow the course of these two currents is only 

 51, or about 44 per cent, of the whole — a proportion, it need scarcely be said, 

 which could not obtain, if it be the case that there is a general flow of the atmo- 

 sphere at the surface of the earth in the northern hemisphere from the tropics 

 towards the north pole, and from the north pole towards the tropics. 



Further, if the two maximum directions be separately examined, it is seen 

 that the greater maximum direction being from any point of the compass from 



S.S.W. to W. occurs at 47 stations. 

 W.N.W. to N. ,, 33 

 N.N.E. to E. „ 19 „ 



E.S.E. to S. „ 16 „ 



and the lesser maximum direction being from any point from 



S.S.W. to W. occurs at 20 stations. 

 W.N.W. to W. „ 22 



N.N.E. to E. „ 38 



E.S.E. to S. „ 32 



Thus the chief prevailing winds in the north temperate zone blow from some 

 point from S.S.W. to W. at 41 per cent, of the stations, leaving 59 per cent of 

 the stations at which the prevailing winds are from other points of the compass ; 

 and the secondary prevailing winds come from some point from N.N.E. to E. at 

 34 per cent, of the stations, or only a third of the whole. Hence, as in the for- 

 mer case, while the largest percentages of prevailing winds are in the directions 

 in which truly equatorial and polar currents should blow, the percentages from 

 other directions are so large as to preclude the supposition of a general flow of 



