56 future's rtbfracles. 



become feebly incandescent, giving them tbe 

 appearance that we see in a tube that is a 

 partial vacuum when electricity is passed 

 through it. While these auroral displays may 

 be seen almost any night in the far north, 

 they vary greatly in their intensity, so it is 

 only once in a while that they are visible in 

 the temperate latitudes. 



What are called magnetic storms occur 

 occasionally, and at such times the telegraph 

 service will sometimes be paralyzed on all the 

 east and west lines for many hours. Strong 

 earth-currents will flow east and west, and be so 

 powerful and so erratic that it is sometimes 

 impossible to use the telegraph. It sometimes 

 happens that the operators can throw off their 

 batteries and work on the earth-current alone. 

 Sometimes it is necessary to make a complete 

 metallic circuit to get away from the influence 

 of the earth in order to use the telegraph. Cur- 

 rents equal to the force of 2,000 cells of 

 ordinary battery have been developed some- 

 times in telegraph wires. This of course is a 

 mere fraction of what is passing through the 

 earth under the wire through which the cur- 

 rent flowed. On the 17th and 18th of Novem- 

 ber, 1882, a magnetic storm occurred that ex- 

 tended around the globe, as it was felt 

 wherever there were telegraph wires. These 

 magnetic storms are attended by brilliant dis- 

 plays of the aurora, and this fact strengthens 



