Thus the Berlin-Dresden line was directed about 8½° east of south, and the Berlin-Thorn line somewhat more to the north of east. The latter line had a length about 2.18 times that of the former. The resistances in the two lines were made the same, so if we suppose the difference of potential between earth plates along a given direction to vary as their distance apart, the current observed in the Thorn-Berlin line has to be divided by 2.18 to be comparable with the other. In this way, resolving along and perpendicular to the geographical meridian, Weinstein gives as proportional to the earth currents from east to west and from south to north respectively

J = 0.147i′ + 0.435i, and J′ = 0.989i′ − 0.100i,

where i and i’ are the observed currents in the Thorn-Berlin and Dresden-Berlin lines respectively, both being counted positive when flowing towards Berlin.

It is tacitly assumed that the average earth conductivity is the same between Berlin and Thorn as between Berlin and Dresden. It should also be noticed that local time at Berlin and Thorn differs by fully 20 minutes, while the crests of the diurnal variations in short lines at the two places would probably occur about the same local time. The result is probably a less sharp occurrence of maxima and minima, and a relatively smaller range, than in a short line having the same orientation.

Table I.

Mean Diurnal Inequalities for the year. Numerical Values of resultant
current.
Greenwich. Thorn-Berlin-Dresden. Thorn-Berlin-Dresden.
Hour. North
to
South
(Mag.)		 East
to
West
(Mag.)		Berlin
to
Dresden.		 Thorn
to
Berlin.		North
to
South
(Ast.)		 East
to
West
(Ast.)		Mean hourly values from
Year. Winter. Equinox. Summer.
1 −94 −41 −17 −13 −20 −10 81 94 51 98
2 −68 −24 −6 −13 −9 −11 84 115 39 97
3 −44 −8 −1 −1 −1 −1 84 113 31 108
4 −18 +9 −20 +15 −17 +17 101 94 58 127
5 −30 −1 −79 +21 −74 +32 122 58 78 230
6 −63 −33 −139 +5 −136 +26 148 80 139 225
7 −121 −80 −138 −36 −144 −14 166 155 206 136
8 −175 −123 −7 −98 −28 −92 203 152 185 271
9 −156 −137 +249 −156 +212 −184 305 67 272 575
10 −43 −77 +540 −184 +494 −254 557 232 628 811
11 +82 +1 +722 −165 +678 −-263 728 411 885 887
Noon +207 +66 +673 −107 +642 −200 675 441 848 735
1 +245 +94 +404 −20 +395 −79 400 284 510 406
2 +205 +113 +35 +55 +46 +47 98 68 103 125
3 +153 +97 −261 +99 −237 +132 272 136 355 324
4 +159 +108 −397 +114 −368 +167 404 218 503 492
5 +167 +118 −391 +108 −363 +160 397 206 453 532
6 +125 +95 −311 +96 −287 +137 319 176 333 446
7 +43 +55 −237 +85 −216 +115 247 180 250 312
8 −22 +4 −191 +74 −173 +98 201 207 217 181
9 −115 −49 −168 +59 −153 +81 174 208 194 120
10 −138 −74 −135 +40 −125 +58 138 155 149 111
11 −136 −70 −84 +18 −79 +29 89 64 95 107
Midnight −147 −80 −43 −2 −43 +4 91 42 119 111

It was found that the average current derived from a number of undisturbed days on either line might be regarded as made up of a “constant part” plus a regular diurnal inequality, the constant part representing the algebraic mean value of the 24 hourly readings. In both lines the constant part showed a decided alteration during the third year—changing sign in one line—in consequence, it is believed, of alterations made in the earth plates. The constant part was regarded as a plate effect, and was omitted from further consideration. Table I. shows in terms of an arbitrary unit—whose relation to that employed for Greenwich data is unknown—the diurnal inequality in the currents along the two lines, and the inequalities thence calculated for ideal lines in and perpendicular to the geographical meridian. Currents are regarded as positive when directed from Berlin to Dresden and from north to south, the opposite point of view to that adopted by Weinstein. The table also shows the mean numerical value of the resultant current (the “constant” part being omitted) for each hour of the day, for the year as a whole, and for winter (November to February), equinox (March, April, September, October) and summer (May to August). There is a marked double period in both the N.-S. and E.-W. currents. In both cases the numerically largest currents occur from 10 A.M. to noon, the directions then being from north to south and from west to east. The currents tend to die out and change sign about 2 P.M., the numerical magnitude then rising again rapidly to 4 or 5 P.M. The current in the meridian is notably the larger. The numerical values assigned to the resultant current are arithmetic means from the several months composing the season in question.

7. The mean of the 24 hourly numerical values of the resultant current for each month of the year a deducible from Weinstein’s data—the unit being the same as before—are given in Table II.

Table II.—Mean Numerical Value of Resultant Current.