62 
MR. W. H. BARLOW ON THE SPONTANEOUS ELECTRICAL CURRENTS 
all. There were some exceptions to this rule, but they were rare, and always of 
short duration. 
The spontaneous deflections of the telegraph needles had been observed on other 
lines of railway as well as on the Midland, and they had been attributed to atmo- 
spheric electricity passing by the wire through the coil to the earth, or vice versa 
from the earth to the atmosphere. This supposition was apparently strengthened, 
because during thunder-storms it has frequently occurred that the wires in the coils 
have been fused, the poles of the needles reversed, or the needles de-magnetized ; 
but it is difficult to conceive any effect of atmospheric electricity that would account 
for the relative positions of the needles of the telegraphs proceeding from Derby 
northwards as compared with those proceeding southwards*. 
My attention was strongly drawn to the subject by the constancy of these effects, 
when a circumstance occurred which imparted a new interest to the inquiry. On 
the evening of the 19th of March, 1847, a brilliant aurora was seen, and during the 
whole time of its remaining visible, strong alternating deflections occurred on all the 
instruments. Similar effects were observed also on the telegraphs on several other 
lines of railway. 
Regarding with much interest these effects, which appeared to open a new field for 
investigation, I determined on making a systematic set of observations on the subject. 
Each of the lines of telegraph centring at Derby consists of several wires ; from 
Derby to Birmingham, and Derby to Rugby, there are five wires. From Derby to 
Lincoln there are three wires, and from Derby northwards there are seven wires. 
At the time of commencing these experiments only three wires had been put in 
operation for telegraph business. There were two spare wires of the railway tele- 
graph from Rugby and Derby, and thence to Leeds, unoccupied, and two others from 
Birmingham to Derby and from Derby to Normanton belonging to the Telegraph 
Company, and intended to form a portion of the commercial telegraph, which were 
also at liberty. 
I applied to Mr. Hatcher, the engineer of the Telegraph Company, for permission 
to make use of their spare wires in the proposed experiments, which was freely 
accorded ; and I am much indebted to this gentleman and to Mr. Culley, under 
whose management the Midland districts is placed, for the valuable assistance and 
information they have afforded me in this inquiry. 
My first object was to make two delicate galvanometers, which was readily accom - 
plished by making use of the “ detectors” employed in ascertaining any defect in the 
insulation of the wires. 
These instruments are similar in principle to those employed in working the tele- 
graph, having a coil of fine wire about 1000 feet in length, in which an astatic needle 
* Since this was written I have received a communication from Mr. Culley, in which he points out an im- 
portant distinction between the effects of lightning and the aurora on the instruments of the telegraph needles, 
which I beg to add as a postscript to this paper. 
