260 History of Luminescence 



At several later times Franklin expressed the same idea and in 

 April 14, 1779 addressed the French Academy on the subject. 



The relation between aurorae and electricity was generally recog- 

 nized after the middle of the century. Wm. Watson in 1752 re- 

 marked how electric discharges in evacuated tubes " resembled very 

 much the lively coruscations of the aurora borealis." John Canton 

 (1753) also wrote: " Is not the aurora borealis the flashing of elec- 

 trical fire from positive toward negative clouds at a great distance 

 through the upper part of the atmosphere where the resistance is 

 least? " Later he declared (1754) that he had never seen the air 

 outdoors at night to be electrical " except when there has appeared 

 an aurora borealis, and then to but a small degree." He gave as 

 additional proof of electrical origin the fact that 



electricity is now known to be the cause of thunder and lightening; 

 that it has been extracted from the air at the time of an aurora borealis, 

 that the inhabitants of northern countries observe the aurora to be re- 

 markably strong when a sudden thaw happens after severe cold weather; 

 and that the curious in these matters are now acquainted with a sub- 

 stance that will without friction, both emit and absorb the electric fluid, 

 only by the increase or diminution of its heat. . . . 



This substance was tourmalin, whose thermoelectric or pyroelectric 

 properties were discovered by Aepinus (1724-1802) in 1756. G. B. 

 Beccaria (1758) also considered the aurorae electric in origin. 

 Finally, Joseph Priestley (1769: 353) disposed of the relation of 

 aurorae and electricity by writing: "That the Aurora Borealis is 

 an electrical phenomenon was I believe never disputed from the 

 time that lightning was proved to be one." ^^ 



An alleged connection between aurorae and the weather has been 

 noted by almost everyone, and became so fixed in the minds of 

 observers that a Mr. J. W. Winn in 1774, in a letter to Benjamin 

 Franklin, published in the Phil. Trans, of that year, cited twenty- 

 three cases in which an auroral display in England had invariably 

 been followed by a southwest gale. The kind of weather predicted 

 was by no means uniform, varying from hot to cold, and from hurri- 

 canes and stormy weather to " beau temps " depending on the experi- 

 ence of the person making the prediction. 



^' The Abb^ Bertholon de Saint Nazaire (died 1799) , who wrote the excellent 

 article, " Aurore boreale," for the Dictionnaire de physique of the Encyclopedie 

 methodique in 1793, expressed the same generally accepted view at the end of the 

 century, that the aurora was a " lumi^re phosphorico-^lectrique." He assembled eight 

 principles characteristic of electricity or the " electric fluid " in support of this view. 



