104 I^IE. C. V. WALKEE ON MAONETIC STOEMS AND EAETH-CTTEEENTS. 
must flow in order to be collected in the two wires in question, and in the direction given, 
as follows:— 
No. 13 . , . 90 — 72 = 18 W. of N. ; the northern limit. 
No. 17 . . , 90— 2 = 88 E. of N. ; the southern limit. 
106 ; the total range. 
This range is shown by the shaded part of fig. 3 ; and is 74° less than that of fig. 2. 
In times of greater activity (and these are very frequent) we have the case shown in 
fig. 4. Besides No. 13, which, as I have said, is always present, we have, as before, on 
the one hand No. 17, the Margate — Bamsgate group, and on the other No. 26, the 
Dover — London group. The azimuths here are far wider apart. By treating them as 
before, setting otf 90° from either toward the other, we have 
No. 26 . . . 90 — 44=46 E. of N.; the northern limit. 
No. 17 . . . 90 — 2 = 88 E, of N.; the southern limit. 
42 ; the total range. 
We get here within a comparatively narrow range, and begin to discover the approxi- 
mate parts of the horizon whence the currents come. The shaded parts of fig. 4 show 
this graphically. I have not thought it necessary to give these figures in duphcate in 
order to show the cases in which all the currents are reversed; it will be readily 
gathered that, mutatis mutandis, the results would be shown by a shaded part in the 
opposite quadrant. 
Table XII. contains, in sections 1 and 2, a selection of a few out of the multitude of 
simultaneous observations that have been made, and which give the results shown in 
fig. 4. The years 1857, 1859, and 1860 have contributed samples. I might extend this 
Table at pleasure. It will be remarked that not only have we here the direction in 
which the derived currents were moving in the telegraph lines No. 17 and No. 26, or 
then’ converse. Nos. 18 and 25 ; but we have also the evidence that currents were moving 
in a similar direction along many distinct lines of telegraph, the bearings of which with 
the magnetic meridian are intermediate between the two extremes given. For example ; 
by comparing fig. 4 with fig. 1, it will be seen that all these other groups, taken from 
Table XI. and entered in Table XII., fall between the two radii marked 17 and 26;. 
they are in order N. 5, 13, 15, 32 and 28; so that we have here a large series of 
observations taken over a considerable area of country, each confirming the accuracy of 
the other, and all conspiring to prove that the point of the horizon from which the 
earth-currents came in 1857, as well as in 1860, was situated somewhere between 46° 
and 88° E. of the magnetic north. I have in the several columns entered the values of 
the currents in the wordi of the observers. They are sufiiciently characteristic. 
On December 17, 1857 (which, by the by, was at the period of the earthquake that 
committed so much devastation in the kingdom of Naples, and of which a Keport was 
presented to the Eoyal Society by Mr. K. Mallet, on May 24, I860*), the earth- 
* Proceedings of the Eoyal Society, vol. x. p. 486. 
