134 COSMOS. 



at the Cape of Good Hope, and more especially at the island 

 of St. Helena, according to the elaborate investigation of Cap- 

 tain Younghusband. At Toronto the principal disturbances 

 generally occurred in the period from midnight to 5 A.M.; 

 it was only occasionally that they were observed as early as 

 from 10 P.M. to midnight, and consequently they predomin- 

 ated by night at Toronto, as well as at Hobarton. After 

 having made a very careful and ingenious investigation of 

 the 3940 disturbances at Toronto, and the 3470 disturbances 

 at Hobarton, which wereincluded in the cycle of six years 

 (from 1843 to 1848), of which the disturbed variations con- 

 stituted the ninth and tenth parts, Sabine was enabled to 

 draw the conclusion* that " the disturbances belong to a 

 special kind of periodically recurring variations, which fol- 

 low recognizable laws, depend upon the position of the sun 

 in the ecliptic and upon the daily rotation of the earth round 

 its axis, and, further, ought no longer to be designated as irreg- 

 ular motions, since we may distinguish in them, in addition to 

 a special local type, processes which affect the whole earth." 

 In those years in which the disturbances were more frequent 

 at Toronto, they occurred in almost equal numbers in the 

 southern hemisphere at Hobarton. At the first-named of 

 these places these disturbances were, on the whole, doubly as 

 frequent in the summer namely, from -April to September 

 as in the winter months, from October to March. The 

 greatest number fell in the month of September, in the same 

 manner as at the autumn equinox in my Berlin observations 

 of 1806-t They are niore rare in the winter months in all 

 places ; at Toronto they occur less frequently from Novem- 



* Sabine, in the Phil Transact, for 1851, pt. i., p. 125-127. " The 

 diurnal variation observed is, in fact, constituted by two variations 

 superposed upon each other, having different laws, and bearing differ- 

 ent proportions to each other in different parts of the globe. At trop- 

 ical stations the influence of what have been hitherto called the irreg- 

 ular disturbances (magnetic storms') is comparatively feeble ; but it is 

 otherwise at stations situated as are Toronto (Canada) and Hobarton 

 (Van Diemen's Island), where their influence is both really and pro- 

 portionally greater, and amounts to a clearly recognizable part of the 

 whole diurnal variation." We find here, in the complicated effect of 

 simultaneous but different causes of motion, the same condition which 

 has been so admirably demonstrated by Poisson in his theory of waves 

 (Annales de Chimie et de Physique, t. vii., 1817, p. 293). "Waves of 

 different kinds may cross each other in the water as in the air, where 

 the smaller movements are superposed upon each other." See La- 

 mont's conjectures regarding the compound effect of a polar and an 

 equatorial wave, in Poggend., Annalen, bd. Ixxxiv., s. 583. 



t See p. 130. 



