468 REPORT— 1881. 



the photograpliic magnetic records have never before been collected from 

 other stations, and there has been no opportunity of comparing them. 

 From the precise similarity of the forms of the curves in many cases, we 

 may say that the rate of change of magnetic disturbances at widely distant 

 stations is the same. There is nothing fitful or flashing in such disturb- 

 ances as these of March 26. We might imagine a current in the crust of 

 the earth, or a current or transfer of electricity in the air near to, i.e. within 

 twenty or thirty miles of, each of these observatories, but to imagine the 

 same current and the same variations of the current at so many different 

 stations all changing in the same way at the same instant is difficult, 

 unless it can be shown in what way all these changes are connected with 

 the cause of such a regular electric discharge. It seems easier to imagine 

 that such changes as these are due to a change produced by induction in 

 the magnetism of the earth itself by some distant body. 



Sometimes disturbances occur where at the same instant there are 

 similar deflections of the declination needles at stations wide apart, and 

 suddenly at one of the stations the needle no longer continues to move 

 with the others, but begins to go, and continues for a considerable period 

 to go, in the opposite direction to the others, turning when they turn, and 

 tracing out a similar curve, but turned always in the opposite direction. 

 Such cases occurred frequently during March 1879, and especially on 

 March 23, about 1.30 and about 7 p.m. Kew time, and on March 29 about 

 9 p.m. 



During the month of August 1880, a very good opportunity occurred 

 for studying a grand magnetic storm, which was accompanied by brilliant 

 displays of Aurora and by earth -currents. This storm began on August 

 11, and lasted until the 14th, and may be divided into three distinct storms 

 — one lasting from 10.20 a.m. (G.M.T.) on the 11th to 1 a.m. on the 12th ; 

 a second from 11.30 a.m. on the 12th to 7.20 a.m. on the 13th ; and the 

 third from 11.50 a.m. on the 13th to 7 a.m. on the 14th. Smaller disturb- 

 ances fill up the interval between the second and third storms. 



Four plates have been prepared from very careful tracings from the 

 photographic records at the several observatories. In the cases of Toronto 

 and Zi-ka-Wei the time-scales are not the same as at Kew, and the curves 

 have been taken from carefully drawn curves which have been plotted on 

 the Kew scale. The plates show the principal portions of the three 

 storms. The beginning of the first storm (August 11) is marked at all 

 stations by a sudden considerable increase in the horizontal force. 

 (Plate X.) At Kew the beginning of the storm is not actually re- 

 corded, because a new sheet was being put on the cylinder at 10.20 a.m., 

 when the storm was beginning. The Kew deflections are smaller than 

 the others, because the horizontal force needle at Kew was less sensitive 

 than the others, the scale-values being -00127 mm. mg. for 1 mm. at Kew, 

 as compared with -00029 mm. mg. for 1 mm. at St. Petersburg. The 

 storm begins at the same instant in Europe, Asia, and America, in high 

 northern and southern latitudes, and also near the equator at Bombay, 

 and everywhere precisely in the same way. It may also be traced at 

 the Mauritius, and there are very distinct similarities of form between 

 the Mauritius and Lisbon curves. The practical value of the curves 

 at the Mauritius and at some other stations is greatly diminished, because 

 the needles do not appear to be sufficiently sensitive to show the character 

 of the magnetic changes. 



During the early part of the storm, on August 11, after the first de- 



