Electroluminescence 263 



how a magnet could affect the Uiminous phenomena in a gas at low 

 pressure, when electric discharges were passing through the tube. 



Spectral investigations of the aurora appear to have been first 

 made by Anders Jons Angstrom (1814-1874) , astronomer at Upsala, 

 who discovered (in 1869) the green line, whose origin subsequently 

 aroused so much discussion. He also found three weak lines in the 

 blue region. 



Ignis Lamb ens and Ignis Fatuus 



NATURE OF THE PHENOMENON 



The ignis lambens or licking fire has excited as much superstition 

 as the aurora but of a more personal kind, since the silent electrical 

 discharge is often associated with human beings. Ignis lambens is 

 without doubt an electroluminescence, but is sometimes confused 

 with ignis fatuus or foolish fire, a phenomenon much less definite, 

 which may have a variety of origins, as indicated below. 



Practically every early writer on " meteores " and the nature of 

 things included ignis lambens and ignis fatuus in the discussion, for 

 example J. Jonston, in Thaumatologia Naturalis (1632, 1657). Like 

 their celestial counterparts, these appearances were attributed to 

 " exhalations." The point of view is well expressed in the account 

 from the Speculum Mundi (Cambridge, 1635) , written by John 

 Swan (fl. 1630) , as follows: 



Ignis lambens is a cleaving and licking fire or light; and is so called 

 because it useth to cleave and stick to the hairs of men or beasts, not 

 hurting them, but rather (as it were) gently licking them. These flames 

 may be caused two wayes, as the learned write. 



First, when clammie Exhalations are scattered abroad in the aire in 

 small parts, and in the night are set on fire by an Antiperistasis; '^^ so 

 that when any shall either ride or walk in such places as are apt to 

 breed them, it is no wonder that they stick either on their horses, or - 

 on themselves. 



Secondly, they may be caused another way, vis. when the bodies of 

 men or beasts, being chafed, do send out a fat and clammie sweat; which 

 (according to the working of nature in things of this kinde) is kindled 

 and appeareth like a flame. 



Ignis fatims, or foolish Fire (so called, not that it hurteth, but feareth 

 or scareth fools) is a fat and oily Exhalation hot and drie (as all Exhala- 

 tions are which are apt to be fired) and also heavie in regard of the 



^* Antiperistasis—" Antagonism of natural qualities, as of light and darkness, heat 

 and cold; specifically, opposition of contrary qualities by which one or both are 

 intensified, or the intensification so produced." Century Dictionary, 1891. 



