Magnetic Variations at different Places, #c. 203 



tion magnet was drawn towards the west, the north end of the hori- 

 zontal force magnet towards the north, nnd the north end of the 

 vertical force magnet downwards ; the sign indicating in each 

 case the opposite movement. At Mauritius, Batavia, and Melbourne, 

 at which places the south end of the needle dips, the sign + indicates 

 that the south end of the vertical force magnet was drawn down- 

 wards. In the absence of definite information, this is presumed to 

 apply also to Cape Horn, at which the south end also dips. The 

 movement in horizontal force appears to have been in general the 

 most significant. At -the stations in tropical regions the movements 

 in declination and vertical force were usually small. 



The table gives an interesting synopsis of the direction of magnetic 

 movement in the several cases, and the genera*! similarity of movement 

 at each station on different days. Thus the movements in the three 

 magnetic elements on different days at Cape Horn, Bombay, Batavia, 

 and Zi-ka-wei were, so far as information is available, in each case 

 similar throughout, and, with one or two exceptions, also at Greenwich, 

 Pawlowsk, and Mauritius ; at Melbourne there were variations, and 

 at Toronto, for which place information in regard to the declination 

 change only was received, there were also variations. At Greenwich 

 the increase in all elements was always accompanied by earth current 

 of one character as respects direction of current, the instances of 

 decrease in the magnetic elements being accompanied by earth cur- 

 rent of opposite character. 



The general, indeed remarkable, similarity in the character of the 

 initial magnetic impulse on different days at the several places, con- 

 sidered in connexion with the coincidence in time, indicates the advent 

 in these cases of some powerful disturbance or sudden shock influencing 

 the magnetism of the whole earth nearly always in the same way, an 

 influence in which the earth becomes, as it were, at once involved, a 

 state of general magnetic calm being at all places immediately con- 

 verted into a state of magnetic activity. Whether these magnetic 

 movements occur more frequently when any particular region of the 

 earth is turned towards the sun is a question that the selected cases 

 of Table I, with the additional instances to be found in Table IV, are 

 too few to determine ; but this point may receive elucidation from a 

 more extended inquiry which the many years of Greenwich records 

 will readily afford, and with which object some tabulation thereof 

 has been already made. 



Our inquiry has been confined to a consideration of the initial mag- 

 netic movements preceding disturbance. As pointed out, these move- 

 ments occur simultaneously, both for the different magnetic elements 

 and for all places. The character of the magnetic change is mostly 

 similar at any one place on different days, but is not necessarily the 

 same for all places ; that is to say, the initial* phenomena become, on 



