470 



Correlation betiueeii Barometric Heights. 



first nodal line there will be positive correlation, beyond it negative 

 correlation, until we reach the second nodal line ■ beyond this the corre- 

 lation may become again positive, and so on. All nodal lines appear 

 to be relative to a given station, and are not to be considered as curves 

 peculiar to the earth's surface. 



One important result of this system of places nodal to a given 

 station is, that it probably depends on the interval of time between 

 the observations at the two stations. Accordingly, in endeavouring to 

 predict the height of the barometer on the east side of the Atlantic 

 from an antecedent series of heights on the west side, we might easily 

 fail to get satisfactory results if the stations on the west side were 

 approximately nodal to one or more stations on the east side. In this 

 case we might do better to take our stations further to the west, or nearer 

 the maxima of the next internodal zone. 



We hope shortly to complete our calculations to the Cape, and then 

 to finish the work already begun on the American stations. Mean- 

 Avhile, we think that the correlation of a series of stations following 

 roughly a parallel of latitude across Europe and Russian Asia would 

 throw a flood of light on whether a chain of roughly north and south 

 stations differs wholly in character from a chain of east and west 

 stations. The magnitude of the computations, however, almost pre- 

 cludes the idea that any individual worker or workers can hope to 

 complete such a task within a reasonable period. 



