132 COSMOS. 



I must not pass without notice, consisted in the very rare 

 occurrence of a vertical motion, a kind of tilting motion, an 

 alteration of the inclination of the northern point of the 

 needle, which was continued for a period of from fifteen to 

 twenty minutes, accompanied by either a very moderate de- 

 gree of horizontal vibration or by the entire absence of this 

 movement. In the careful enumeration of all the secondary 

 conditions which are recorded in the registers of the English 

 observatories, I have only met with three references to " con- 

 stant vertical motion, the needle oscillating vertically,"* and 

 these three instances occurred in Van Diemen's Land. 



The periods of the occurrence of the greater magnetic 

 storms fell, according to the mean of my observations in 

 Berlin, about three hours after midnight, and generally ceased 

 about 5 A.M. We observed lesser disturbances during the 

 daytime, as, for instance, between 5 and 7 P.M., and fre- 

 quently on the same days of September, during which vio- 

 lent storms occurred after midnight, when, owing to the 

 magnitude and rapidity of the oscillations, it was impossible 

 to read them off or to estimate the means of their elonga- 

 tion. I soon became so convinced of the occurrence of mag- 

 netic storms in groups during several nights consecutively, 



tion that they indicate whether the vibrations and shocks are "strong" 

 or "slight," and characterize the disturbances in accordance with defin- 

 ite and uniform subdivisions of the scale, following a fixed and uni- 

 form nomenclature. Sabine, Days of Umisual Magn. Disturbances, 

 vol. i., pt. i., p. 4G. Six groups of successive days (146 in all) are 

 given from the two above-named years in Canada, which were marked 

 by very strong shocks, without any perceptible change in the horary 

 declination. Such groups (see Op. cit., p. 47, 54, 74, 88, 95, 101) are 

 designated as " Times of Observations at Toronto, at which the magnetom- 

 eters loere disturbed, but the mean readings were not materially changed^'' 

 The changes of variation were also nearly ahvays accompanied by 

 strong vibrations at Toronto during the frequent Auroras Boreales ; in 

 some cases these vibrations were so strong as entirely to prevent the 

 observations from being read off. We learn, therefore, from these 

 phenomena, whose further investigation we can not too strongly rec- 

 ommend, that although momentary changes of decHnation which dis- 

 turb the needle may often be followed by great and definite changes 

 of variation (Younghusband, Unusual Distwbances, pt. ii., p. x.), the 

 size of the arc of vibration in no respect agrees with the amount of 

 the alteration in the declination ; that in very inconsiderable changes 

 of variation the vibrations may be very strong, while the progressive 

 motion of the needle toward a western or eastern declination may be 

 rapid and considerable, independently of any vibration ; and further, 

 that these processes of magnetic activity assume a special and different 

 character at different places. 



* Unusual Disturb. ., vol. i., pt. i., p. 69, 101. 



