THE NEW SCIENCE OF METEOROLOGY 



there were seen horsemen running in the air, in cloth 

 of gold, armed with lances, like a band of soldiers: and 

 troops of horsemen in array encountering and running 

 one against another, with shaking of shields and multi- 

 tude of pikes, and drawing of swords, and casting of 

 darts, and glittering of golden ornaments and harness." 

 Dire omens these; and hardly less ominous the aurora 

 seemed to all succeeding generations that observed it 

 down well into the eighteenth century as witness 

 the popular excitement in England in 1716 over the 

 brilliant aurora of that year, which became famous 

 through Halley's description. 



But after 1752, when Franklin dethroned the light- 

 ning, all spectacular meteors came to be regarded as 

 natural phenomena, the aurora among the rest. Frank- 

 lin explained the aurora which was seen commonly 

 enough in the eighteenth century, though only recorded 

 once in the seventeeth as due to the accumulation of 

 electricity on the surface of polar snows, and its dis- 

 charge to the equator through the upper atmosphere. 

 Erasmus Darwin suggested that the luminosity might 

 be due to the ignition of hydrogen, which was supposed 

 by many philosophers to form the upper atmosphere. 

 Dal ton, who first measured the height of the aurora, 

 estimating it at about one hundred miles, thought the 

 phenomenon due to magnetism acting on ferruginous 

 particles in the air, and his explanation was perhaps the 

 most popular one at the beginning of the last century. 



Since then a multitude of observers have studied the 

 aurora, but the scientific grasp has found it as elusive in 

 fact as it seems to casual observation, and its exact 

 nature is as undetermined to-day as it was a hundred 



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