| Description | Barlow shares observations on certain spontaneous deflections noticed in the needles of the electrical telegraph on the Midland Railway [England]. The signals of the telegraph are made by deflecting a magnetic needle placed in a coil, to the right or left, by means of a galvanic battery.Barlow observes that when no signals were passing, and when the wires of the telegraph were connected with the earth at the two termini, spontaneous deflections, differing in amount and direction, occasionally occurred. He also observes in the four principal lines of telegraph which unite at Derby as a centre, two of which proceed in a northerly direction to Leeds and to Lincoln, and two in a southerly direction to Birmingham and to Rugby, that the relative deflections of the four instruments were such as to indicate that when the current of electricity, which produced the deflection, flowed from Rugby northwards towards Derby, it was also flowing northwards in all the other three; and likewise, that when it flowed southwards in one, it flowed southwards in all; the times of the deflections being simultaneous or nearly so. There appeared to be no regularity as to the hours, either during the day or night, at which these deflections occurred. Atmospheric electricity also affected the instruments, but in general only by sudden and violent effects during thunder storms, sometimes reversing the poles of the needles contained in the coils, and sometimes fusing the wire of the coil itself. Barlow describes how on the night of Friday 19 March 1847, there appeared a brilliant aurora, and during the whole time of its remaining visible, rapidly alternating deflections were exhibited in the telegraph instruments. Barlow undertakes a series of experiments with deflectometers of very delicate construction, and records his results: wires insulated throughout, and wires having only one connection with the earth, produce no deflection; and a complete circuit made by uniting both extremities of two wires, each forty-one miles long, but insulated throughout, produces no deflection. In every case, however, a deflection is obtained on a wire having both ends connected with the earth, the deflection continually varying in amount and sometimes in direction.
Annotations in pencil and ink throughout.
Subject: Magnetism / Electricity
Received 9 June 1847. Communicated by Peter Barlow.
Whilst the Royal Society declined to publish this paper in full, an abstract of the paper was published in volume 5 of Abstracts of the Papers Printed in the Philosophical Transactions of the Royal Society of London [later Proceedings of the Royal Society] as 'On the existence of alternating diurnal currents of electricity at the terrestrial surface, and their connection with the diurnal variation of the horizontal magnetic needle'. |