1902.] Correlation between Barometric Heights. 469 



Standard Deviations in mm. 



Period. 



Bodo. 



Skuclesnaes. 



Valencia. 



Lisbon. 



• 



Funchal. 



1879-88. Summer 



Whole year. . 



7'391 

 11 -056 

 9-551 



7-573 

 11-299 

 9 -588 



7-746 

 10 -50S 

 9-207 



3 -812 

 6-079 

 5-171 



3- 064 



4- 781 

 4-007 



1889-1898. Summer. . . 



,, Winter 



„ Whole year 



7-837 

 10-999 

 9-729 



7-501 

 11-146 

 9-4S2 



7 -227 

 10 -228 

 8-839 



3 393 

 6-253 

 5 -076 



2 -964 

 5 -053 

 4-125 



1879-1898. Summer.. . 



Winter. . . . 

 „ Whole year 



7-640 

 11 -036 

 9-653 



7-545 

 11-223 

 9-537 



7-504 

 10-370 



y -030 



3-609 

 6-175 

 5-127 



3- 015 



4- 919 

 4-066 



winter variability tends to approach the summer variability the further 

 south we go* ; the absolute variability decreasing, however, as we 

 go south. 



Table III. — Correlation of the Barometric Heights at the East Atlantic 



Stations. 



(See attached sheet.) 



Now it will be seen that from these stations, for which our results 

 are very reliable, that 



(i.) The correlation between certain stations is sensibly different 

 for summer and winter. 



(ii.) The correlation varies somewhat for the same pair of stations, 

 from decade to decade. 



(iii.) In every case beyond a certain distance from a station the 

 correlation becomes negative, reaches a negative maximum, and then 

 begins to decline. 



Now we refrain from either plotting curves for these changes in cor- 

 relation or from drawing inferences as to the nature of the instan- 

 taneous distribution of barometric height along a meridian until we 

 have been able to deal with more complete data from equatorial 

 stations, and from stations south of the equator. But we believe this 

 alternation of instantaneous high and low barometer! along a meridian, 

 and the discovery of uncorrelated stations, are of sufficient physical 

 interest to deserve immediate notice. We propose to call a station, 

 uncorrelated with a given station, a station nodal to it. Thus to every 

 station will exist a first nodal line of stations, the barometric height at 

 which is uncorrelated with that at the given station. Within this 



* There is an apparent exception to this in Bodo and Skudesnaes. 

 + " High " and " low " barometer at any station mean here above and below the 

 mean for that station. 



