148 History of Luminescence 



with an Impetus, as Oil of Vitriol distilled from its weight of Nitre, and 

 then mix'd with twice its weight of Oil of Anniseeds. . . . 



Qu. 9. Is not Fire a Body heated so hot as to emit Light copiously? 

 For what else is a red hot Iron than Fire? And what else is a burning 

 Coal than red hot Wood? 



Qu. 10. Is not Flame a Vapour, Fume or Exhalation heated red hot, 

 that is, so hot as to shine? For Bodies do not flame without emitting a 

 copious Fume, and this Fume burns in the Flame. This Iqnis Fatuus 

 is a Vapour shining without heat, and is there not the same difference 

 between this Vapour and Flame, as between rotten Wood shining with-' 

 out heat and burning Coals of Fire? 



Newton was thus fully aware of the various kinds of lumines- 

 cences, and, like others of his time endeavored to explain them by 

 reference to a common cause, in his opinion the " vibratory motion 

 of their parts," applicable to all luminous bodies both hot and cold. 

 It is not in the origin of light but in his view of the propagation of 

 light, as a stream of particles, that Newton differed from Descartes, 

 and also from his contemporaries, Hooke and Huygens, the sup- 

 porters of a wave-like propagation. 



Summary 



Thus, before 1700, all the main types of luminescence save one 

 (crystalloluminescence) were recognized, and a very considerable 

 body of facts regarding their properties had been accumulated. Some 

 new luminous animals had been recognized. With the growing 

 disuse of Latin as a scientific language, and the rapid spread of 

 knowledge in every country, the stage was set for the many detailed 

 studies of luminescent phenomena characteristic of the coming years. 

 New examples of all types of luminescence were to be discovered 

 and new facts assembled. The great goal ahead was explanation of 

 the cause of the light emission, a fitting aim for scientists who fol- 

 lowed the pioneers of the seventeenth century. 



