152 History of Luminescence 



insects in hot countries, and worms in oysters; also rotten wood, 

 hair, scales, feathers, blood, and flesh of animals at certain times 

 and certain circumstances. Eyes, such as those of Alexander the 

 Great which shone like fire, and the tongue of the viper " which 

 seems on fire when the animal is irritated," were also classed as 

 natural phosphores; likewise, the diamond, rubbed on gold; gold, 

 silver, and copper rubbed on glass, as observed at the French 

 Academy of Sciences in 1707; sulphur and sugar when crushed, 

 water of the sea in tempests and in the wake of ships. 



De Mairan remarked that some explained the light of the sea as 

 reflection of moonlight or starlight but he declared that the sea 

 actually had a light of its own. The only other marine luminescent 

 body mentioned was the " poulmon marine " (jellyfish) which some 

 thousrht to be a fish and others claimed to be a " viscous excrement 

 of the sea hardened by the sun." ^ 



Finally, among the " phosphores naturelles " were those phe- 

 nomena which consist of sulphurous exhalations and inflame in the 

 air, the " Ardens " or " feux folets " on the hair of horses or on 

 infants, or on trees. They were called St. Elmo's fire by sailors. In 

 addition, the occasional displays of " feux aeriens " (the aurora 

 borealis) , especially bright in 1683, were grouped as natural phos- 

 phores. This list has a strong resemblance to one published by 

 Francis Bacon. 



Among artificial phosphores, de Mairan mentioned the burning 

 phosphorus of Kunkel, the Bolognian Stone, the hermetic phos- 

 phorus of Baudouin, the phosphorus of Romberg, and the light of 

 mercury in a barometer or in a pneumatic machine, i. e., a vacuum. 

 According to de Mairan, the explanation of all these luminescences 

 lay in movement of the sulphur which they contained. The ordi- 

 nary cause of this movement was fermentation, external agitation, 

 rubbing or fire. The movement had to be great enough to dis- 

 engage the sulphur from material which hampered it. The density 

 and cohesion of this material was regarded as an impediment to the 

 movement until the sulphur transmitted some of its motion to its 

 surroundings and " broke from its prison," when light appeared. 

 Matter that contained much sulphur luminesced by fermentation 

 alone, such as flesh, the skin of " testaceous fishes " and exhalations 

 in the air. The luminescence of animal material after death and of 

 wood that luminesces when it is rotten, were regarded as the best 

 examples of light fiom fermentation. 



The glowworm and other living animals could not become lumi- 

 nous unless circulation of a nourishing fluid, agitation of the spirits 



* F. Bacon apparently held this view. 



