OF ATMOSPHERIC PRESSURE IN EUROPE^ ETC. 263 



breaking up of the periodical trade winds or monsoons in 

 the China Sea and Indian Ocean. It is probable, there- 

 fore, that the two systems of phenomena are directly con- 

 nected with and dependent upon each other; and as the 

 changes of the monsoons are known to be sometimes very 

 irregular it will become an interesting subject of inquiry 

 to ascertain whether corresponding irregularities occur in 

 the disturbances of the atmosphere in the middle and 

 higher latitudes of Europe and Asia. 



Although probably not bearing directly upon the subject 

 of this paper, I may perhaps be allowed to draw attention 

 to a very decided convexity of nearly all the curves in the 

 month of October, in two or three cases producing a small 

 maximum. Indications of a similar irregularity in the 

 month of March are also apparent in some of the curves. 

 These features clearly indicate the operation of a secondary 

 disturbing cause acting during those mouths, but more 

 especially during October, over the whole breadth of 

 the two continents, and therefore probably differing alto- 

 gether in its nature and origin from the disturbing cause 

 which produces the two great movable maxima. 



It may be well to state that the mean monthly values 

 given in the table have not been corrected for the dif- 

 ferences in the lengths of the months; but corrected 

 values would not materially affect the general results, and 

 it was not considered necessary in a preliminary inquiry 

 to adopt months of equal length, or to calculate the mean 

 daily amount of oscillation for each month. 



In concluding this brief account of results which seem 

 to me to indicate clearly the existence of a regular law of 

 atmospheric disturbance in regions of the earth which have 

 hitherto been generally regarded as remarkable for the 

 apparent irregularity of their atmospherical phenomena, I 

 cannot omit to mention the fact that the first application 

 of the method of reduction which has led me to these 



