NATURAL PHILOSOPHY. 151 



TELEGRAPH LINES AND THE AURORA BOREALIS. 



Mr. George B. Pi*escott, well known as an electrician and 

 author of valuable works on the telegraph, makes the following 

 interesting explanation of a phenomenon noted in the case of 

 a recent auroral display : — 



'* On the evening of the 15th of April a magnetic storm of un- 

 usual force prevailed over the entire northern section of the coun- 

 try, which so seriously affected the operation of the wires that, 

 on some circuits, they could only be worked by taking off the 

 batteries and employing the auroral current instead. The effect 

 of this great disturbance of the earth's magnetism was manifested 

 with particular power upon the wires between New York and 

 Boston, and for several hours the lines upon this route depended 

 entirely upon this abnormal power for their working current. 

 During the prevalence of this storm, however, I operated upon 

 two wires between the above cities by a plan which rendered 

 them as free from the effects of these earth cuiTents as a local 

 circuit. 



"Everyone has observed that the auroral cm'rent comes in 

 waves of ever-changing polarity, corresponding in length and 

 direction with the scintillations of the visible aurora. Sometimes 

 these waves continue but a few seconds, and sometimes for a 

 longer time ; but their constant change of polarity prevents the 

 successful operation of a wire, because at one moment the auro- 

 ral wave may augment the strength of current on the line, while 

 at the next it entirely neutralizes it. Therefore, it has frequently 

 been found advisable to remove the batteries entirely, and work 

 with the auroral current alone. But the operation of the lines in 

 this manner is very unsatisfactory, owing to the uncertain and 

 fitful character of this force ; and, therefore, any feasible plan by 

 which the wires may be worked under such circumstances is 

 worthy of adoption. 



" The plan by which I overcame the diflficulties arising from 

 the disturbance of the earth's magnetism was by disconnecting 

 two wires from the earth at Boston, and connecting them to- 

 gether, while I grounded them both at New York, thus forming 

 a loop extending from New York to Boston. As the two wires 

 were both upon the same supports, the auroral wave travelled over 

 each in the same direction, and, by uniting the two wires at one 

 end, the auroral influence upon one wire was made to neutralize 

 that upon the other, and thus the wires were left entirely free. 



'* Of course it makes no difference how often the polarity of 

 the auroral cuiTcnt changes, or how much the strength of this 

 current may vary, since the direction of the current, and its 

 strength, change as much upon one wire as the other, and there- 

 fore the current upon one always exactly equals and neutralizes 

 the other." 



