PART I. ON MAGNETIC STORMS. CHAP. II. 



139 



of the arrows in lower latitudes is then occasioned by the eastward movement of the storm-centre along 

 the auroral zone, with the principal axis always keeping its direction (see p. 94). When it is desired 

 to verify on all the charts this movement of the storm-centre during the course of the perturbation, it is 

 necessary, as we have said several times, to remember that the size of the current-arrows at the four 

 Norwegian stations, is not always a certain guide to the position of the storm-centre (see p. 137). This 

 travelling of the storm-centres is possibly caused by the effect of terrestrial magnetism upon the current- 

 system, and by the alteration in the earth's magnetic axis during the perturbation. We shall return to 

 this subject later on. 



TABLE XXI. 

 The Perturbing Forces on the 26th December, 1902. 



TABLE XXI (continued). 



TABLE XXI (continued). 



