64 
MR. W. H. BARLOW ON THE SPONTANEOUS ELECTRICAL CURRENTS 
travel along the wires from one earth connection to the other, alternating first in one 
direction and then in the other. 
In examining the results obtained from this experiment, there appeared a general 
movement of the needle to the right from the commencement of the observations in 
the morning until midnight, then changing over to the left until nine or ten o’clock 
in the morning, when it again passed to the right, large and rapidly alternating deflec- 
tions having occurred during the night, the effects of which were visible on the ordi- 
nary telegraph instruments. The general direction of the needle, however, indepen- 
dently of these irregular influences, appearing to exhibit some regularity, I followed 
up the experiments with the galvanometer at Derby, and found that a similar motion 
of the needle occurred daily. 
This discovery led me to establish a series of observations for fourteen days and 
nights, on two wires simultaneously, one from Derby to Birmingham, and the other 
from Derby to Rugby, the position of the needle being recorded every five minutes, 
day and night. The mean position of the needles during each hour, as obtained 
from these observations, is given in Tables Nos. I. and II., and the mean result for 
each week is given in the right-hand column. 
The path described by the two needles during the week, ending May 29, 1847, is 
also exhibited in the diagram No. 2. 
In order to explain the directions in which the currents traversed the wires in these 
experiments, it is necessary to state that the two extremities of the coil in the galva- 
nometers are attached to two brass screw pegs, technically called ‘‘terminals,” which 
stand up on the top of the case of the galvanometer, one on the left hand and the 
other on the right, and the coil was so arranged that when the copper pole of a 
battery was connected with the left hand terminal, and the zinc pole with the right, 
the deflection (which in all cases refers to the upper end of the needle) was to the 
left ; and assuming that the cui rent flows from the copper to the zinc pole, a deflec- 
tion to the left in these observations indicates a current flowing along the wire 
towards Derby, and a right-hand deflection shows the current to be flowing from 
Derby to the extremity of the wire. 
In addition to the above-mentioned experiments, simultaneous observations were 
made with galvanometers on the wires proceeding from Derby northward and south- 
ward, the results of which showed that the currents producing the regular diurnal 
deflections followed the same law as to their relative directions in the four different 
lines of telegraph centring at Derby, as that which had been observed on the tele- 
graph instruments during periods of the large spontaneous deflections. 
The broad feature elicited by these observations may therefore be stated to be, — 
1st. That the path described by the needle consisted of a regular diurnal motion, 
subject to disturbances of greater or less magnitude. 
2nd. That this motion is due to electric currents passing from the northern to the 
southern extremities of the telegraph wires, and returning in the opposite direction. 
