ON MAGNETIC DISTURBANCES AND EARTH-CURRENTS. 469 



flection, the general direction of the Toronto deflections is opposed to those 

 at tbe other stations ; but from 4 p.m. to 8 p.m. (G.M.T.), i.e. from about 

 10.40 a.m. to 2.40 p.m. Toronto time, the deflections are alike, and in the 

 same direction at Toronto and at European stations. (See Plate XI.) 

 Again, about 11 p.m., there is a very violent phase of the storm, in which 

 the deflections are alike and in the same direction at Toronto, Zi-ka-Wei, 

 and at the European stations. 



There is considerable similarity in the form of the Toronto horizontal 

 force curve and the Melbourne declination curve for the beginning of the 

 storm. There is also a remarkably close agreement between the horizontal 

 force curves at Kew and at Vienna during the storm, the diff"ereuces in 

 the amount of the deflections being due to the fact that the needles are 

 not equally sensitive. The horizontal force curves at Kew and Bombay 

 also agree very closely during the first four hours of the storm, after which 

 the Bombay needle shows very little action. 



The second storm, beginning about 11.30 a.m. (G.M.T.) on the 12th, 

 and lasting until the next morning, was the most remarkable of the three. 

 Plate XII. gives the changes in the magnetic elements from 10 a.m. on the 

 12th to 1 a.m. on the 13th. At about 11.40 a.m. the disturbances begin to 

 become violent, and from 12 to 1 they are so great that in some cases the 

 paper is not wide enough to receive the record, and in others the paper is 

 either not sensitive enough to record the impressions or is so blackened 

 that it is impossible to trace the form of the record upon it. The hori- 

 zontal force trace at Toronto and the declination trace at Kew go ofl" 

 the paper. At Melbourne and at Vienna the trace fails. 



At the time of greatest disturbance, 12.25 p.m., it is very remarkable 

 that at Lisbon and at Zi-ka-Wei near Shanghai, in China, two places 

 nearly in the same latitude but about nine hours apart in time, the 

 vertical force is increased in precisely the same way and to about the 

 same amount at the same instant. There is also a striking similarity 

 between the Melbourne and the Zi-ka-Wei horizontal force curves and 

 between the Zi-ka-Wei and Kew declination curves. 



At Zi-ka-Wei the sudden change in the horizontal force amounted to 

 about -033 m.m.-m.g. units, or t-jVo*^ P^i"*- of ^^^ ^'Ot^l horizontal force. At 

 St. Petersburg the change in the horizontal force amounted to '04 m.m. 

 m.g. units, or ^^^th part of the whole horizontal force, and the total force 

 was changed by about ^^tb part of its full value. This second storm is 

 remarkable for the very great diminution in the vertical force at St. 

 Petersburg. Prom ,5.30 p.m. to 12.30 (local time), the vertical force 

 diminishes by -06 (m.m. m.g.), the horizontal force in the same interval 

 diminishing by "04 (m.m. m.g.) 



There are also remarkable points of agreement during the storm, as 

 may be seen by a careful comparison of the curves, but the agreement 

 between St. Petersburg horizontal and vertical force curves compared 

 with Kew and Lisbon declination curves is remarkable about 4.30 p.m. 

 and between 7 and 8 p.m., when the change in the horizontal force in 

 about ten minutes at St. Petersburg amounted to -027 m.m. m.g. units 

 or o\yth of the horizontal force. 



With the Lisbon declination curves there is some uncertainty, as the 

 times of the beginning and end are not marked upon the tracing, and the 

 time-scale does not appear to be quite the same as for the horizontal or 

 vertical force curves. 



Thus we see that the magnetic changes which take place at various 



