136 COSMOS. 



which 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 15 to 20 

 minutes, accompanied by either a very moderate degree of 

 horizontal vibration or by the entire absence of this move- 

 ment . In the careful enumeration of all the secondary condi- 

 tions which are recorded in the registers of the English obser- 

 vatories, I have only met with three references to " constant 

 vertical motion, the needle oscillating vertically," 71 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 3 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 violent 

 storms occurred after midnight, when, owing to the magni- 

 tude and rapidity of the oscillations, it was impossible to read 

 them off or to estimate the means of their elongation. I 

 soon became so convinced of the occurrence of magnetic 

 storms in groups during several nights consecutively, that I 

 acquainted the Academy at Berlin with the peculiar nature 

 of these extraordinary disturbances, and even invited my 

 friends to visit me at predetermined hours, at which I hoped 

 they might have an opportunity of witnessing this pheno- 

 menon, and in general I was not deceived in my anticipa- 



turbed, but the mean readings were not materially changed." The changes 

 of variation were also nearly always accompanied by strong vibrations 

 at Toronto during the frequent Aurora 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 cannot too strongly recommend, that although 

 momentary changes of declination which disturb the needle may often 

 be followed by great and definite changes of variation (Younghusband, 

 Unusual Disturbances, 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 towards 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. 

 N Unusual Disturb, vol. i, pt. i, pp. 69, 101. 



