PART HI. EARTH CURRENTS AND EARTH MAGNETISM. CHAP. I. 79 1 



We here give the results of the comparisons of synchronous serrations. 



P P 



^KW 2 ' 59 millivolt IFeyg '' 4 ' 32 millivolt 



p * P d 



:o. 5 8 :o.8 7 



Je s\\-' Je .\s 



EARTH-CURRENTS IN ENGLAND. 



159. We have also received from Greenwich photographic copies of registerings of earth-currents 

 md the horizontal magnetic elements for a number of selected days. They are given in PI. XXXVI to 

 XXXVIII, XLI and XLII. 



We also give a series of examples of storms taken from curves of 1883, published in the Green- 

 wich Observatory Reports. The curves selected are taken from various periods, but principally from 

 he more recent years, from which there are also observations from other stations. One example in- 

 :luded is from AIRY'S observations, namely, a storm on the aist September, 1866. 



In the more recent years the earth-current curves are so greatly perturbed by wandering currents, 

 hat in the majority of cases only the night registerings are of importance to our investigations. 



If we now look at these registerings from the same points of view as before, we see in the first 

 >lace that it is chiefly only one of the earth-current curves, the ^4-curve, that has powerful deflections. 



It further appears that the deflections in the two components very nearly go together. It is, how- 

 ver, difficult to follow the details, partly on account of the apparently slight sensitiveness, and partly 

 >ecause of the strong, disturbing influence of local causes. 



It therefore seems as if the direction of the current here once more remains fairly constant, and 

 hus in accordance with the conditions at Kaafjord and in East Germany. 



Here too, as at Pare St. Maur, an automatic arrangement introduces exactly synchronous time- 

 larks into all the curves. 



If we now attempt to compare the earth-current curves with the magnetic curves, we find that 

 ic conditions here appear to be more variable than those of the two sets of registerings previously 

 escribed. If we first look at the storm of the 2ist September, 1866, we there find the induction phe- 

 omenon extremely distinct when we compare the earth-current curve Greenwich-Croydon with the D- 

 urve; while in the //-curve there is evidently a very marked effect of the earth-currents, the deflections 

 i the two curves appearing very nearly to go together. 



The other earth-current component, Greenwich to Dartford, exhibits only very small deflections. 



In the next storm, however, on July 21 and 22, 1889, the D and H curves seem to have changed 

 lies. The deflections in earth-current and declination seem to be very nearly synchronous, while on 

 omparing the earth-current curves with the //-curve, we find displacements which indicate induction- 

 henomena. 



Conditions such as those in the first of these two are found strongly marked in a number of 



ases, e. g. the storms of 



March 26 27, 1883, 



October 5, 1883, 



October 16, 1883, 



November i 2, 1893, 



January n 12, 1894, 



November 24 25, 1894, 



November 78, 1893. 



