On Diurnal Variation of Barometric Pressure. 25 



A=Lt ^ftçi(r)dr, (23) 



B large ^-^ "g 



where L, is the area of land in a circular belt with the radius r and 

 the breadth dr. 0(r) is to be considered as a function of r which 

 continuously tends to zero for the large value of r. Let be prac- 

 tically zero for r>i?o, then 



^ = -Î- fEr (r) dr = M?M.fL, dr (24) 



where ^ is a fraction between and 1. But the factor of 0(<?ü!o) is 

 what we have called the continentality in the preceding paragraphs, 

 if Ro could be put^lO°. The value of 6 varies of course from 

 station to station. For an equal value of the integral, d will be 

 greater or less according as the land is concentrated near the centre, 

 or near the margin of the area in question. The case in which the 

 land is convex toward the sea will have a greater A than the case 

 when it is concave, ^ being the same for both cases. It has been 

 found in the first part of the paper that ai for Western European 

 stations are generally small compared with that for the stations in 

 the other continents, with nearly the same K. This may of course 

 be explained chiefly by the effects of the prevailing West wind 

 from the Atlantic, but probably also partly by the fact that for most 

 of these stations the water surface is found intruding more or less 

 near the central part of the circular area. 



10. Thus far, we have treated exclusively the annual means 

 of the diurnal amplitude and took no notice of the rather remark- 

 able variability during the course of a year. Angot applied the 

 method of harmonic analysis for representing the annual variation 

 of «1 as well as of ^i, the results of which are tabulated in his 

 memoirs cited. On actually plotting the monthly values of a^ and 

 (pi in diagrams, however, we came to the conviction that for a large 

 number of stations, the annual variation is so irregular that the 

 real physical significance of only the first terms of Fourier's ex- 

 pansion seems quite doubtful, being small compared with the terms 

 of higher orders left out. It seemed to us interesting to review 



