430 SCIENTIFIC RECORD FOR 1882. 



will allow measures to be matle). Tliis first motion was to decrease 

 the west declination and increase the horizontal force at both places. A 

 bold motion in the two Zi-ka wei carves at 11.30 A. 3i. (increase of dec- 

 lination, decrease of horizontal force) has corresponding decrease of 

 horizontal force at Greenwich, not accompanied, however, by much mo- 

 tion in declination. And of numerous fluctuations occurring at Green- 

 wich, between noon and midnight of the same day, some appear to 

 correspond with motions at Zi-ka-wei whilst others do not. 



A calm state follows at both ] daces until near noon of August 12. 

 Upon this day at about 11.40 A. 31. the magnets at Greenwich made 

 a further start, and until 4 p. 51. Ihe movements were large. A corre 

 sponding start is also shown in both the Zi-ka-wei curves, commencing, 

 according to the register, some minutes sooner than at Greenwich, the 

 movements following being similarly large. Afterwards, until G A. m. 

 of August 13, considerable oscillation was nearly continually shown at 

 Greenwich, there behig especially a large change of declination between 

 7 and 9 P. M. (August 12) ; but there is no strongly marked motion at 

 the latter time at Zi ka-wei, and the changes throughout are much 

 smaller than at Greenwich. Later, on August 13, further oscillations 

 occur at both places, but the separate motions are in no particular 

 accordance. This period of disturbance seems to definitely come to an 

 end at both places at 6 A. m., August 14. 



A period of quiet is broken at Greenwich August 18, at 1.45 P. m., 

 by a sharp though small movement both in declination and horizontal 

 force (increase of both). There is a corresponding sharp inctease 

 (after quietude) of horizontal force at Zi ka-wei, but no change of decli- 

 nation. A bold increase of declination and decrease of horizontal force 

 at Greenwich, 7 A. m. of August 19, is accompanied by a similar de- 

 crease of horizontal force at Zi-ka-wei, but with little change of decli- 

 nation. Bolder changes occur at the latter place at noon, but with 

 comjjaratively .^mall change at Greenwich. The magnets become quiet 

 at both jdaces at or near midnight, August 19. 



The general result of this comparison of Greenwich and Zi-ka-wei 

 curves appears to be that, after a quiet period, the first indication of a 

 disturbance, if sudden (it need not be large), occurs simultaneously or 

 nearly so at both places, but that during the continuance of disturbance 

 the oscillations of the magnets seem to be so locally modified that it 

 becomes difflcult to trace correspondence: some movements appear to 

 corresi)ond and some not. A strongly marked bend in the trace at one 

 place may appear, as it were, stunted in that at the other place, or may 

 not be perceptible at all. The disturbances api)ear to die out at prettj^ 

 much the same time at both places. All this confirms very much what 

 Mr. Whipple has pointed out as regards Melbourne. [Nature^ xxii, 

 p. 558.) 



M. Dechevrens of Zi-ka-wei, in some remarks which accompany the 

 sheet of curves, notes that the disturbance of August 11-14 is the great- 



