MAGNETIC DISTURBANCES. 



ber till February, and at Hobarton from May till August. 

 At St. Helena and at the Cape of Good Hope the periods at 

 which the sun crosses the equator are characterized, accord- 

 ing to Younghusband, by a. very decided frequency in the 

 disturbances. * 



The most important point, and one which was also first 

 noticed by Sabine in reference to this phenomenon, is the 

 regularity with which, in both hemispheres, the disturbances 

 occasion an augmentation in the eastern or western varia- 

 tion. At Toronto, where the declination is slightly west- 

 ward (1 33'), the progression eastward in the summer, that 

 is, from June till September, preponderated over the pro- 

 gression westward during the winter (from December till 

 April), the ratio being 411:290. In like manner, in Van 

 Diemen's Land, taking into account the local seasons of the 

 year, the winter months (from May till August) are charac- 

 terized by a strikingly diminished frequency of magnetic 

 storms.* The co-ordination of the observations obtained in 

 the course of six years at the two opposite stations, Toronto 

 and Hobarton, led Sabine to the remarkable result that, 

 from 1843 to 1848, there was in both hemispheres not only 

 an increase in the number of the disturbances, but also (even 

 when, in order to determine the normal annual mean of the 

 daily variation, 3469 storms were excluded from the calcu- 

 lation) that the amount of total variation from this mean 

 gradually progressed during the above-named five years from 

 7 / -65 to lO'-oS. This increase was simultaneously percepti- 

 ble, not only in the amplitude of the declination, but also in 

 the inclination and in the total terrestrial force. This result 

 acquired additional importance from the confirmation and 

 generalization afforded to it by Lament's complete treatise 

 (September, 1851) "regarding a decennial period, which is 

 perceptible in the daily motion of the magnetic needle." 

 According to the observations made at Gottingen, Munich, 

 and Kremsmunster,t the mean amplitude of the daily dec- 



* Sabine, in the Phil. Transact, for 1852, pt. ii., p. 110 (Younghus- 

 band, Op. cit., p. 169). 



f According to Lamont and Kelshuber, the magnetic period is ten 

 years four months, so that the amount of the mean of the diurnal mo- 

 tion of the needle increases regularly for five years, and decreases for 

 the same length of time ; on which account the winter motion (the 

 amplitude of declination) is always twice as small as the summer mo- 

 tion (see Lamont, Jahresbericht der Sternwarte zu Mitnchenfur 1852, 

 s. 54-60). The director of the Observatory at Berne, Rudolph Wolf, 

 finds, by a much more comprehensive series of operations, that the 



