-I o 



( -^1 ) 



purpose) a constant difference in diiection /// bclwecn (he niaxiniuni 

 values of those quantities, as defined by (10) and therefore dependent 

 upon the friction {k) and variable with the order of the period (q). 

 If the angle of deviation were known, the value of k and hence 

 the friction coefticient hi might he deduced from (10). 



3. If we calculate the diurnal variation of the barometric height 

 for different places on the earth's surface, it appears that the 

 monodiurnal variation widely differs, as to amplitude and phase, in 

 the different seasons and that it shows great divergences for places 

 as near to each other as de Bilt, Helder, and Vlissingen. 



TABLE I. 

 Diurnal variation of barometric height (1902—1910). 



de Bilt. 



mm. mm. 



Winter 0.0447 cos {nt — 178°) + 0.1805 cos (2 nt — 295°) 

 Spring 0.0097 cos {nt — 177°) + 2049 cos (2 nt — 301 

 Summer 0.0238 cos {nt - 79°) + 0.1665 cos (2 nt ^ 311 

 Autumn 0.0305 co.v (/z/ — 135°) -f 0.2001 m§ (2 ?2i; — 296°) 

 Year 0.0214 cos {nt — 147°) + 0.1864 cos (2 nt — 300°) 



Helder. 



Winter 0.0431 cos {nt — 93°) -f 0.1976 cw (2 /z^ — 309°) 



Spring 0.1942 cos {nt — 59°) + 0.2087 cos {2 7it~3[3°) 



Summer 0.2200 cos (nt — 59°) + 0.1856 my (2 ?if — 324°) 



Autumn 0.1391 cos{nt— 72^) + 0.2255 cos {2 nt — '^04:') 



Year 0.1472 cos {nt — 65°) + 0.2038 tuy (2 yz^ — 313') 



Vlissingen. 



Winter 0.1321 w.s' (/i^ — 190 ) + 0.2079 cos {2 nt — 315°) 



Spring 0.0369 cos {nt — 49°) + 0.2268 cos (2 nt — 308^^) 



Summer 0.0994 cos {nt — 55 ) + 0.2109 cos (2 nt—'è\l°) 



Autumn 0.0267 co.y («^ — 122°) + 0.2366 cos (2 nt — '60T) 



Year 0.0314 cos {nt — 121°) + 0.2196 cos (2 nt — 312°) 



The semidiurnal variation on the contrary, extensively in\ estigated 

 in well known memoirs bv Hann and A>(;ot, shows a remarkable 

 uniformity, the ami)litude legularly decreasing from about 1 mm. 

 near the equator to the |)oIe ; at Batavia the ihiily vai-iation caji be 

 represented by the expressioji : 



4* 



