446 Magnetic Variations, Magnetic Disturbances, fyc. [May 5 ? 



being those of Toronto, Greenwich, Pawlowsk, Mauritius, Bombay, 

 Batavia, Zi-ka-wei, and Melbourne, and, for a less number of days, 

 Cape Horn (as obtained from the Mission Scientifique du Cap Horn, 

 1882-83). It was desired to have times for Pola, but it was found 

 that photographic registers during great part of the period did not 

 exist. The variation in time at each place from the mean of times 

 for all places is given for each day. The mean deviation at the 

 different places varies from + 2"4 minutes to — 2'9 minutes, the 

 agreement between four of the places, Greenwich, Pawlowsk, Mauri- 

 tius, and Bombay, being very much closer, the mean values of devia- 

 tion for Greenwich, Pawlowsk, and Bombay differing, indeed, by only 

 Ol minute, equivalent to 6 seconds. 



The question arises, Are the differences real, or due (considering 

 the contracted time scale) to accidental error ? If the magnetic im- 

 pulse is really simultaneous over the whole earth, it is a striking- 

 physical fact, and if not entirely so, the circumstance is no less 

 interesting ; but greater attention to accuracy of time scale, or a more 

 extended scale, may be necessary before the point in question can be 

 definitely settled. 



A table is added, showing the character of the magnetic movement 

 at the several observatories, from which it appears that at any one 

 place the movements on different days were in most cases similar, 

 though different at different places, indicating on these occasions the 

 occurrence usually of one general type of disturbance. 



Reference is made to the question of earth currents. A comparison 

 for thirty-one days, between 1880 and 1891, of cases of sudden mag- 

 netic movement and earth current, shows the earth current to pre- 

 cede the magnetic movement by 0*14 minute, equivalent to 8 seconds. 

 The question of the relation between magnetic movements and earth 

 currents is discussed. 



The desirability of being able temporarily to obtain, when occasion 

 requires, a more extended time scale for all magnetical and meteoro- 

 logical phenomena is pointed out. 



The general result is that in the definite magnetic movements pre- 

 ceding disturbance the magnets at any one place are simultaneously 

 affected ; also that in places widely different in geographical position 

 the times are simultaneous, or nearly so, a small constant difference 

 existing at some places which may be real or may be accidental, but 

 the character of which it seems desirable to determine. It is shown 

 also that at Greenwich definite magnetic movements are accompanied 

 by earth current movements which are simultaneous, but that neither 

 magnetic irregularities nor ordinary magnetic variations seem to 

 admit of explanation on the supposition of being produced by the 

 direct action of earth currents 



