On Eapid Periodic Variations of Terrestrial Magnetism. 



19 



Fig. 6, B {ditto). 



clockwise (N-E-S) after a certain hour near midnight. This seems 

 just as if the magnetic disturbing vector, initially inclined to the 

 meridian, rotates in the sense to l^ecome parallel to the meridian. 



Characteristic disturbances of the above type are met with 

 most frequently just at midnight. In other hours, especially near 



IBS' cases occur not 

 Fig. 6, A (^ original size). ^^rely where an abrupt 



Xote the parallelism between X and Z. increase of the llOri- 



zontal component is 

 not accompanied with 

 any conspicuous train 

 of waves. 



It is a very re- 

 markable fact that 

 even for these abrupt 

 nonperiodic disturb- 

 ances of long duration, 

 the Z-component 



follows the various 

 fluctuations of the 

 X-component with 

 utmost faithfulness, 

 except for a reduced 

 amplitude and a 

 definite retardation. 

 This characteristic 



behaviour served as a 

 very convenient means 

 for disentangling the 

 cliaos of photographic 

 traces in the records 

 of disturbed days. 



At the beginning of 

 the al)ruptly starting 

 train of waves, the 

 amplitude is some- 



T'emark the a^jparent " beat " of the waves in tlie 

 lower curves. 



Fig. Ü, C {ditto). 



