THE AURORA BOREALIS. 475 



At troubled seasons in antiquity and the middle ages, in times of 

 war, famine, or epidemic, the only sentiment the aurora excited was 

 that of fear, and the people thought they could see in the sky rivers 

 of blood, armies clashing, and infantry and cavalry engaging in mys- 

 terious combats. Now, except among a few superstitious or unin- 

 formed persons, the phenomena are witnessed with simple curiosity 

 by some, with indifference by others. 



A thousand years after Gregory of Tours, who gave the meteor 

 the name it now bears, Gassendi first examined it with a scientific 

 eye, and definitively baptized it on the 12th of September, 1621. The 

 terms " polar light " and " northern light," which have been proposed 

 by various physicists, have never prevailed ; the bishop and the phi- 

 losopher have triumphed. From the beginning of the eighteenth cen- 

 tury, observations became more numerous, and theories and scientific 

 discussions began to appear. The subject even tempted the poets. To 

 say nothing of the Abbe Delille, an Italian Jesuit, Father Noceti, sung 

 the aurora in Latin verse. Frazier, in 1712, first witnessed a southern 

 aurora. 



It is afiirmed that the aurora was not common in Scandinavia 

 and Holland previous to about 1716, after which it began to appear 

 more frequently. Whether this be so or not, the attention of several 

 Swedish, Dutch, and French investigators was fixed upon it. Celsius, 

 the designer of the centigrade thermometer, remarked the curious dis- 

 tractions to which compass-needles were occasionally subject, without 

 visible cause ; studying the perturbations more closely, he had no diffi- 

 culty in assuring himself (1741) that they coincided with the appear- 

 ance of the aurora borealis. Hjorter, another Swede, made the same 

 observation at about the same time. 



The question whether auroras are of cosmic origin, or whether they 

 proceed from purely terrestrial influences, which still provokes dis- 

 cussion, has from the beginning divided the learned into two parties. 

 Mairan maintained the extra-terrestrial character of the meteor, while 

 the contrary opinion found a supporter in Musschenbroek, the inventor 

 of the Ley den- jar. 



Musschenbroek, still evidently under the influence of old middle- 

 age prejudices, gave out the following hypothesis : Near both poles, 

 and at a little distance beneath the surface of the globe, are immense 

 reservoirs of phosphorescent matter. Whenever a fissure is formed 

 reaching to them, the substances, readily volatile, escape and illumi- 

 nate the atmosphere with their glow. The frequency of auroras in 

 particular years was explained by supposing a subterranean cavern to 

 have been opened. When the pocket was exhausted, the phenomenon 

 would of course be at an end for some time. So, after the exhaustion 

 of the provisions of phosphorescent stuff accumulated in a particular 

 region, the meteors would necessarily cease to show themselves, not to 

 appear again till after a long time, during which the matter would ac- 



