1904] Time Factor on Correlation between Barometric Heights. 413 



considerable correlation between the barometric readings on successive 

 days at the same station. Moreover, it is possible that the correlation 

 between the daily rise or fall at different stations might give better 

 results for prediction than the correlation between the actual heights 

 observed ; but what has already been done is sufficient to indicate the 

 manner in which modern statistical methods may aid the meteorologist 

 in this part of his work. As regards the more fundamental, though 

 less immediately useful, task of meteorological science, the intervals of 

 maximum correlation, a few examples of which have been considered in 

 this paper, will, I believe, be found ultimately to be of importance in 

 relation to the physics of the atmosphere. Although considerable 

 labour is involved in the calculation of these intervals, even for a 

 single pair of stations, yet the increase of theoretical knowledge which 

 would result from an adequate investigation of the manner in which 

 they depend upon local conditions, and upon the positions and 

 distances of the places considered, would probably be amply sufficient 

 to justify the labour expended upon the matter. 



8. The conclusions to be drawn from the results given in this paper 

 are as follows : 



(i) The correlation between the barometric readings at two stations 

 upwards of 1000 miles apart depends upon the interval between the 

 readings. In the case of Halifax and Wilmington, the correlation is 

 sensible for at least 9 days, and it reaches a maximum for an interval 

 of about 16 hours in summer and 23 in winter. For these stations, 

 and also for St. Helena and Cape Town, the observation at the more 

 easterly station should be taken later for maximum correlation. 



(ii) There is a considerable correlation between the daily rise at 

 Halifax and Wilmington, and this correlation changes with the interval 

 in a manner somewhat analogous to that in which the correlation 

 between simultaneous heights at two stations approximately on the 

 same meridian depends upon the distance between them. 



(iii) There are considerable differences between the summer and 

 winter correlations, and these differences are of the same general 

 nature for both pairs of stations considered. 



(iv) It is possible to predict the barometric height at one station 

 from an earlier height at a second station more than 1000 miles away, 

 with a fair degree of accuracy, the mean observed error for forty dates, 

 taken at random, for Halifax and Wilmington, being 0"'15. 



