PART III. EARTH CURRENTS AND EARTH MAGNETISM. CHAP. I. 793 



'axis in the same direction as before. The direct effect of the earth-currents upon the magnetic appa- 

 ratus is here more difficult to trace, but seems to be noticeable especially on comparison of the H and 

 E W curves, where the induction-phenomenon is not quite so distinct as in the other components. 



As far as can be concluded from the observations at our disposal, it would appear that the same 

 chief peculiarities are to be found in the earth-current conditions at Pawlowsk as at the stations pre- 

 viously studied. 



The distinctness of the induction-phenomenon in both components here, may be partly due to the 

 rather more northerly situation of this station, partly to the probably homogeneous nature of the soil there. 



We cannot, as we have said, have any well-founded opinion as to whether the circumstances here 

 pointed out are the usual ones, as we have so few curves to refer to. 



COMPARISON OF SIMULTANEOUS EARTH-CURRENT OBSERVATIONS. 



161. In selecting the storms given here, we have, in a number of instances, paid especial regard 

 to those cases in which we have simultaneous observations from several places. In this way we can 

 obtain some idea of the course of the earth-currents within a somewhat larger district. A number of 

 such cases are shown in the Plates. 



Of two days we have simultaneous observations from Germany, France and England, these days 

 being November i 2, 1883, and November 5 6, 1883. The observations from France are Blavier's 

 and are published in his previously-mentioned work. As, however, his curves for the first of these 

 ^torms are exceedingly jagged and their course in consequence not very clear, we have here given 

 :opies only of the second perturbation. It will be seen that there is a very great resemblance between 

 :he earth-current curves in Germany and the one earth-current component in France, namely, the curve 

 r or the line Paris to Dijon. We here find a very striking resemblance both in the principal course of 

 ;he strong deflection that, as we have seen in Germany, indicates the effect of induction from the outer 

 system, and in a number of details. 



As regards the details, I can only point to a number of undoubtedly synchronous serrations, which 

 ire numbered on the various curves with figures from i to 10. 



The change in the principal deflection of this current-component takes place at any rate almost 

 simultaneously with the change in Germany. 



The effect of the earth-current upon the horizontal magnetic elements cannot unfortunately, as in 

 jermany, be eliminated, as the point of light at the time of the maximum had passed out of the field; 

 )ut it seems probable, from the course of the curves, that if such elimination had been effected, the 

 esult arrived at would have been the same as in Germany, as all the characteristics of Weinstein's, 

 curves are also found here. The change in the earth-current component takes place a little while after 

 he Z)-curve has reached its maximum, and just at a place where the descending branch of the curve 

 las an outward bend exactly similar to that found on the curve at Wilhelmshaven, and which we con- 

 sidered to be probably produced by the more marked direct effect from the outer systems where the 

 .fleet of the earth-current was only slight. 



It will be seen that in the line Paris to Dijon a shunt of ] /40 of the galvanometer's resistance is 

 ;mployed, while in the others a shunt of J /20 > s employed. 



As the resistance in the lines is very nearly equal, and the distance between the earth-connections 

 ilso approximately equal, we see from this that if the deflections in the various curves were to be 

 ompared, those in the line Paris to Dijon would have to be imagined increased to twice the number. 

 vVe then see that it is the currents in this line that greatly predominate in stength. 



