140 TEERESTRIAL MAGNETISM. 



important of the acquisitions which have been gained towards 

 a complete knowledge of terrestrial magnetism. Sabine 

 has distinguished the disturbances, in the results of both 

 hemispheres, into classes, according to the hours of their 

 occurrence, whether in the day or in the night, the seasons 

 of the year, and the direction in which they deflect the 

 needle, whether to the east or to the west. At Toronto 

 and at Hobarton, the disturbances were twice as great, both 

 in frequency and value, in the night as in the day,( 174 ) as 

 in the older observations at Berlin; but in from 2600 to 

 3000 disturbances at the Cape of Good Hope, and more 

 particularly at St. Helena, the direct contrary was the case, 

 as shown by a similarly thorough investigation of the phse- 

 nomena at those observatories by Captain Younghusband. 

 At Toronto, the principal disturbances were observed, on the 

 average, from midnight to 5 in the morning ; occasionally 

 only they were observed earlier, between 10 P.M. and mid- 

 night, predominating, therefore, in the night at Toronto as 

 at Hobarton. After a very laborious and well-devised examina- 

 tion of 3940 disturbances (of the declination) at Toronto, and 

 3470 at Hobarton, taken from six years of observation, 1843 

 1848, (the observations selected as disturbed making the 

 ninth and tenth portions of the entire mass), Sabine has 

 drawn the conclusion, ( 175 ) that the disturbances belong to a 

 peculiar class of periodically recurring variations, following 

 recognisable laws dependent on the position of the Sun in 

 the ecliptic, and on the diurnal rotation of the Earth upon its 

 axis ; that they ought no longer to be called irregular 

 movements ; and that we may distinguish in them, together 

 with a particular local type, general processes affecting the 

 whole globe. In regard to the different amount of disturbance 

 in different years, the same years in which the disturbances 



