( 316 ) 



simiiltaneons horizontal vectors tbr the arctic stations (after the data 

 given by Lüdeling) lia\e been plotted in a series of 12 maps cor- 



respondhig to the honrs of O's 2^, 4'' 22^ mean Göttingen time. 



These maps revealed the fact that one part of these vectors pointed 

 to one focns and the rest emanated from another. 



The successive places of these foci have been determined as unbiased 

 as possible. Rectangular coordinates have been made use of with the 

 origin in the north pole and taking for ,i; and y axis the meridians 

 180° and 90° E from Greenwich. The unity for the values of the 

 coordinates as given underneath is 2 U/ 0°.5 ; accordingly the value of 

 |/,i'''-}-//^ represents nearly the polar distance in degrees, because 

 the maps have been drawn in stereogTa])hic projection. The focus 

 to which the vectors point has been called a })Ositive focus, that 

 from which they emanate a negative focus. 



Mean — 1.1 —10.7 — 3.4 —10.2 



Harmonic formulae calculated for these four scries : 



|,7" = — 1 .1 -f 13.5 ><ln (t -h 15°) + 2.1 .«hi 2{t + 19^) 

 ly — —10.7 + 14.3 sht {t -[- 14°— 90°) + 2A.nn2{t—2'') 

 ^,i;= _3.4 ^ 18.6 sin {t + 24"+ 1S0°) + 3.2 sin 2 (t-W) 

 ly — _10.2 + 15.7 sin {t + 24^+ 90°) + S.O sin2{t—b0") 



From the constants of these formulae it follows evidently, that both 

 foci move in nearly the same circnlar path Avitli almost constant 

 velocity and with a mutual distance of 180°. 



This being granted and calling .I'a the mean of the .i's for positive 



+ focus 

 — focus 



