MAGNETIC DISTUBBANCES WITH TERRESTRIAL GALVANIC CURRENTS. 471 
agreement. In particular, those which exhibit the irregularities of Northerly Magnetic 
Force are extremely accordant. Yet there are some minor points of discordance, both 
general and special, which merit most careful attention ; and to these I now call the 
attention of the Society. 
The remark of most extensive application is, that the irregularities of the curves 
derived from the Galvanic Currents are more numerous than those derived from the 
Magnetometers. I know not whether this is inherent in the nature or origin of the 
currents, or whether the Magnetic apparatus is less sensitive than the Galvanic apparatus. 
The next remark is, that the irregularities derived from the Galvanic Currents almost 
always precede those derived from the Magnetometers. These intervals of time, as I 
have already remarked, are perfectly certain. There are a few instances (as West Force, 
1867, April 8, 14 h , and June 1, 15 h 50 m ; and North Force, 1867, May 28, 7 h 20 m , and 
June 1, 12 h and 13 h ) in which the Galvanic irregularity appears to follow the Magne- 
tometer irregularity ; and a greater number, especially in the North Force, in which 
their coincidence of time is sensibly perfect ; but in very far the greatest number, the 
Galvanic irregularities precede the Magnetometer irregularities. In the instance of 
West Force, 1866, October 4, 9 h 40 m , and probably in some others, the advance of the 
Galvanic irregularity is nearly half an hour. 
In several instances, the proportions of consecutive rise and fall are not the same in 
the two systems of curves. Thus on 1866, October 4, 5 h to 6 h , the proportions are 
unequal for the West Force, and, in a minor degree, for the North Force. So also for 
the West Force, 1867, May 28, 7 h to 8 U , and June 1, 10 1 * to ll h . In this element, as 
in the times, the accordance is better for the North Force. 
On 1867, June 7, 3 h , there is a remarkable salience of the Galvanometer curve for 
the West Force. Mr. Glaisher suggests an explanation of this which I believe to be 
correct. The circuits had been interrupted in order to make time-marks, and the wires 
had probably taken a galvanic charge, which apparently burst out with great force when 
the circuits were restored. 
On 1867, April 4, West Force, there is discordance which is completely explained by 
ordinary acceleration of Galvanic results and inequality in the proportions of rise and fall. 
On 1867, June 2, West Force, there is discordance of which it is possible the expla- 
nation may be different. The day was the Sunday following the Visitation, and it is 
possible that the instruments may have been disturbed, and that the disturbances may 
not have been corrected. [It is now believed that the movement of the Declination 
Magnetometer was impeded by contact with its box.] 
After all attention has been given to these points, I think that, on repeatedly examining 
the agreements of the two systems of curves, it is impossible to avoid the conclusion 
that the magnetic disturbances are produced by terrestrial galvanic currents below the 
magnets. Yet there remain some points to be explained before we can state that gal- 
vanic currents, as we observe them, will account for all that we observe in the magne- 
tometer records. 
MDCCCLXVIII. 
3 u 
