On Diurnal Variation of Barometric Pressure. 



23 



where x is the nearest distance of the station from the coast con- 

 sidered positive when the station is on the land side of the coast. 

 The above value of ^is of coarse not proportional to x, but nearly 

 so for x<:R, when only veiy rough approximation is concerned. 

 For x:>'R, we have always IC=1. As far as the qualitative verifi- 

 cation of our theory for a stations not very far from the coast is 

 concerned, we must expect that the observed values of «i considered 

 as the function of K will have a minimum near the coast, or for 

 A''=0.5, and two maxima on both sides. To test the point, the 

 data for 33 North American stations were chosen^\ The conti- 

 nentality for each station was evaluated and compared with the 

 corresponding amplitude au Grouping these according to the 

 magnitudes of K, and taking the mean value for each group, we 

 obtained the following result : 



Table VII. 



In Fig. 9. the values of mean ai are plotted, with the mean K as 

 abscissa^\ The result is qualitatively in accordance with the 

 theory, in so far as there is a minimum of a^ near ^"=0.3 or 0.4 

 and two apparent maxima on both side of it. 



If the assumption (20) were actually the case, the values of 



da 



d^a 



and — - would be practically zero for greater value of x and 

 dx dx 



the amplitude m in the interior of a large continent would be the 



same as in the ocean. In the actual case, this latter is never the 



1) Hann, loc. cit.; also Met. Zs., 1899, p. 421. 



2) The curve («i, K) may be considered as transformed from the curve (ai, x) by suitably 

 varying the scale of the abscissa. The value of a^ for 7i =0 is taken from the mean value for 

 Atlantic Ocean 0'-10°N. 



