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LVI. On Earth- currents, and their Connexion with the Phe- 

 nomena of Terrestrial Magnetism. By the Rev. H. Lloyd, 

 D.D., D.C.L.* 



}N the year 1848 Mr. Barlow communicated to the Ptoyal 

 Society a paper " On the Spontaneous Electrical Currents 

 observed in the Wires of the Electric Telegraph/' in which he 

 established the important fact, that a wire, whose extremities are 

 connected with the earth at two distant points, is unceasingly 

 traversed by electric currents, the intensity of which varies 

 with the azimuth of the line joining the points of contact with 

 the ground. The direction of these currents was proved to be 

 the same at both extremities of the same wire, and was shown 

 to depend on the relative positions of the earth-connexions, while 

 it was wholly independent of the course followed by the wire 

 itself. The currents cease altogether when either of the contacts 

 with the earth is interrupted. From these facts Mr. Barlow con- 

 cluded that "the currents are terrestrial, of which a portion is 

 conveyed along the wire, and rendered visible by the multiplying 

 action of the coil of the magnetometer." 



Mr. Barlow further observed that, apart from sudden and 

 occasional changes, the general direction of the needle of the 

 galvanometer appeared to exhibit some regularity. He was thus 

 led to institute a series of observations for fourteen days and 

 nights, on two wires simultaneously, one from Derby to Rugby, 

 and the other from Derby to Birmingham, the positions of the 

 needles in both circuits being recorded every five minutes, day and 

 night. From these observations he concluded — 



"1. That the path described by the needle consisted of a 

 regular diurnal motion, subject to disturbances of greater or less 

 magnitude. 



" 2. 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. 



" 3. That, exclusive of the irregular disturbances, the currents 

 flowed in a southerly direction from about 8 or 9 a.m. until the 

 evening, and in a northerly direction during the remainder of the 

 twenty-four hours." 



He was thus led to examine whether any relation subsisted 

 between these movements and the daily changes of the horizontal 

 magnetic needle. And having made for this purpose a series of 

 simultaneous observations with a delicate declinometer, he came 

 to the conclusion, that although generally the currents flow 

 southwards during that part of the day in which the variation of 



* Communicated by the Author, having been read at a meeting of the 

 Royal Irish Academy, held November 11, 1861. 



