CHANGES DURING A SOLAR-SPOT PERIOD. 



141 



butable to accidental causes. In order, then, to determine 

 whether they are due to the operation of a change in the 

 intensity of solar activity, I have made the following com- 

 parison of the mean pressures under north-east, east, and 

 south-east winds with those under south-west and west 

 winds : — 





Mean pressure, 



under winds 



from N.E., E., 



and S.E. 



Mean pressure, 



under winds 



from S.W. and 



W. 



Difference. 



1858 



in. 



29-848 



29-813 



29-728 



29-775 



29-756 



28-794 



29673 



29-715 



29-664 



29-685 



29-757 



in. 



29649 



29*672 



29-502 



29-714 



29-683 



29-782 



29-717 



29-722 



29-717 



29"835 

 29-748 



in. 



+ 199 



+ •141 

 +'226 

 + •061 

 +•073 



+ -OI2 

 -•O44 

 — •OO7 

 -•053 

 -•150 

 + •009 



i8<;q 



i860 .. 



1861 



1862 



1863 



1864 



1865 



1866 



1867 



1868 



The maximum difference occurred in i860, when solar- 

 spot frequency was at a maximum; and the minimum 

 difference in 1867, when solar-spot frequency was also at 

 a minimum ; and the general course of the differences has 

 a remarkable similarity to that of the numbers representing 

 the variations of solar-spot frequency. 



As the rate of variation in the pressures during the 

 maximum years 1858-62 was greatest in the quadrant 

 between north-west and south-west, and as winds from 

 the westward coming over the Atlantic are probably less 

 affected by disturbing causes than those coming from the 

 eastward over the continent of Europe, it appeared to me 

 that the nature of the law of change of the pressures would 

 be best indicated by a comparison of the differences be- 

 tween the pressures under north-west and south-west winds. 

 These differences are as follows : — 



