6% THK WORLD'S WONDEKS. 



hearing of the aurora, proved that it must have been quite close 

 to the earth. A ball of tire fell during the display, and burst 

 just before it reached the earth, throwing out prismatic scintilla- 

 tions in every direction." 



In January, 1865, Capt. Hall witnessed another aurora even 

 more wonderful than the one above described. The rays of this 

 one were vertical ; it appeared all alive, as if in high glee, 

 dancing to and fro with almost the rapidity of lightning. The 

 three belts extending from southeast to northwest were the most 

 interesting, as they often flashed into the brilliant colors of the 

 rainbow. Each belt occasionally resolved itself into two lines or 

 tiers of rays ; as one line would dance rapidly to windward, the 

 other would dance as quickly in the opposite direction. This 

 extraordinary display lasted five minutes an unusual time. He 

 was so impressed with it that he wrote, " If at home it could be 

 witnessed for one moment, one would say, ' I never saw northern 

 lights before.' " 



That the aurora borealis is due to the earth's magnetism, or a 

 surplus charge of electricity, is most generally believed, though 

 the conditions and result are not clearly understood. Capt. 

 McClintock observed in the Arctic regions that the aurora was 

 never visible above ice fields, but that whenever one was in prog- 

 ress the light appeared always to be gathered over the open water. 

 Water being an excellent conductor of electricity, while ice is a 

 non-conductor, we may infer that the peculiarity observed by 

 McClintock was due to this difference in the conducting powers 

 of ice and water. 



It is held by some that the aurora is due to electrical discharges 

 from the earth. Through some cause the earth, regarded as a 

 vast magnet, becomes overcharged with electrical energy, and it 

 is as this energy is gradually dissipated that the splendors of the 

 aurora are displayed. Prof. Olmstead, however, assigns to the 

 aurora an interplanetary origin. "The nebuluous matter," he 

 reasoned, " like that which furnishes the material of the meteoric 

 showers or the zodiacal light, and is known to exist in the inter- 

 planetary spaces, is probably the cause of the auroral display. 



