i8 



AKSEL S. STEEN. 



.-N. Kl. 



IV. 



The material contained in Table 2 can now first of all be used for 

 studying more closely the diurnal variation of the vector ^'s numerical 

 value. 



During the preliminary construction of the mean x^ector diagrams for 

 Bossekop and Sodankylä for the various seasons (Fig. i, p. u), I became 

 aware of a phenomenon, which, as far as I know, no one has yet pointed 

 out, namely, that the sun's illumination of the magnetic north pole has a 

 decided influence upon the diurnal variations of the horizontal deflecting 

 force. This is clearly seen from Fig. i, where ,in each vector-diagram. 

 I have marked with a black dot on the curve the hour of the local time 

 of the station in question, that corresponds with noon at the magnetic 

 pole, having assumed for the latter a longitude of about 96° W of 

 Greenwich. 



In the summer, when the sun shines upon the magnetic north pole 

 for the greater part of the 24 hours, the curve of the vector-diagram 



