196 Mr. W. Ellis. On the Simultaneity of 



direction Blackheatli North Kent East Junction in the other. The azimuth of 

 the former line, reckoning from magnetic north to east, is 50, and of the latter, 

 reckoning from magnetic north to west, is 46. The direction of strongest earth 

 current at Greenwich is not much different from that of the line joining the 

 A. W. =L. W. earth plates. The current in the A. W. L. W. circuit is always 

 much stronger than that in the B. N. K. E. J. circuit, and a current that causes 

 the A. W. L. "W, trace to more in one direction on the paper causes the 

 B. N. K. E. J. trace to move in the opposite direction. 



these sudden movements, which, although abrupt in character, are 

 sometimes of no great magnitude. There is not the same simul- 

 taneity of movement in the different elements when disturbance 

 commences, as it were, gradually, .or in general during the course 

 of a magnetic storm; the really simultaneous movements are 

 exceptional. 



The annexed Table I contains the times, of commencement of 

 movement on the seventeen selected -days at each of the eight sta- 

 tions. The second column gives the year, day, and hour of disturbance, 

 Greenwich civil time (counting from midnight to midnight), and in 

 following columns are added the times to tenths of a minute for the 

 eight stations, arranged in order of longitude, reckoning from west 

 to east, and reduced to Greenwich time by the application of the 

 differences of longitude given in Table II. From accidental causes, as 

 before mentioned, times were wanting in six cases, and in addition for 

 two in which there were unresolved discordances. These were at 

 Batavia, on 1882, April 16 ; at Pawlowsk and Mauritius, on Ajpril 20 ; 

 at Melbourne, on August 4 ; at Toronto, on September 12 ; at Batavia, 

 on 1883, February 24 ; at Zi-ka-wei, on September 16 ; and at Toronto 

 On 1884, July 2. To maintain a proper balance in the table, times in 

 these cases have been adopted by estimation, paying proper regard 

 to the average deviation of the times at each particular station from 

 the general average of all the stations. 



The times as received were given usually to the nearest minute ; the 

 fractions of a minute that appear in the table are partly due to the time 

 being in most cases the means of those for three magnetic elements, 

 and partly to the fractional value of the longitude used. In a follow- 

 ing column is given for each day the mean of the times at the 

 eight stations, and in succeeding columns the deviation of the time at 

 each station from this daily mean. 



Every instance of magnetic motion included in the table was 

 accompanied at Greenwich by active earth current. It is known 

 that in some cases earth currents were similarly active at other 

 places, and presumably they were active at all places. 



From an inspection of the table it will be seen how nearly these 

 sudden and characteristic magnetic impulses occur at the same 

 absolute time at places geographically widely separated. At some 



