683 



in amount and direction, occasionally occurred. It was also ob- 

 served 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, vv'hich 

 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 south- 

 wards 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 efl^ects during thunder storms, some- 

 times reversing the poles of the needles contained in the coils, and 

 sometimes fusing the wire of the coil itself. But the effects first 

 mentioned appeared to arise from a different cause ; and from the 

 great extent of line affected simultaneously by currents in the same 

 direction, it appeared impossible they could arise from local atmo- 

 spheric influences. On the night of Friday the 19th of March, 

 there appeared a brilliant aurora, and during the whole time of its 

 remaining visible, rapidly alternating deflections were exhibited in 

 the telegraph instruments. 



The occurrence of these phenomena induced the author, with de- 

 flectometers of very delicate construction, to make a series of expe- 

 riments, from which the following results were deduced. Wires in- 

 sulated throughout, and wires having only one connexion with the 

 earth, produced no deflection ; and a complete circuit made by 

 uniting both extremities of two wires, each forty-one miles long, but 

 insulated throughout, produced no deflection. In every case, how- 

 ever, a deflection was obtained on a wire having both ends con- 

 nected with the earth, which deflection was continually varying 

 in amount and sometimes in direction. 



On making a series of observations every five minutes for twenty- 

 four hours, at both extremities of a wire, from Derby to Birming- 

 ham, it was found that the changes, both of amount and direction, 

 occurred simultaneously at the two ends, and that the current flowed 

 from one end communicating with the earth to the other. The 

 examination of this series of observations showed a general 

 direction of the needle to the right from noon till near midnight, 

 and then to the left until between nine and ten a.m., when it again 

 changed to the right. In consequence of this apparent regularity, 

 the experiments were carefully followed up at Derby for a fortnight 

 on the two telegraphic Vv^ires proceeding from Derby to Rugby and 

 Birmingham. These experiments showed that the electric current 

 was subject to a regular diurnal alternation, the times of zero agree- 

 ing nearly with the known times of zero of the variation of the mag- 

 netic needle ; and also that the deflection to the left corresponded 

 with easterly variation, and the deflection to the right with westerly 

 variation ; the path described by the needle of the deflectometer 



