MAGNETIC DISTURBANCES 139 



Toronto they occur less frequently from November 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 characterised, according to 

 Younghusband, by a very decided frequency in the disturb- 

 ances. 



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 variation. 

 At Toronto, where the declination is slightly westward 

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

 from June till September, preponderated over the progression 

 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 A.ugust) are characterised by 

 a strikingly diminished frequency of magnetic storms. 77 

 The co-ordination of the observations obtained in the course 

 of 6 years at the two opposite stations, Toronto and Hobar- 

 ton, 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 calculation,) that the 

 amount of total variation from this mean gradually progressed 

 during the above-named five years from 7 '.65 to 10'.5S. 

 This increase was simultaneously perceptible, not only in 

 the amplitude of the declination, but also in the inclination 

 and in the total terrestrial force. This result acquired addi- 

 tional importance from the confirmation and generalisation 

 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 Kremsmun- 

 ster, 78 the mean amplitude of the daily declination attained its 



77 Sabine, in the Phil. Transact, for 1852, pt. ii, p. 110 (Younghusband, 

 op. cit. p. 169). 



< s According to Lamont and Relshuber, the magnetic period is 

 10 years 4 months, so that the amount of the mean of the diurnal 

 motion of the needle increases regularly for 5 years, and decreases for 



