178 History of Luminescence 



The free admission of air not only produces light in using the phos- 

 phorus of Konkel, but even a blaze of fire where friction is used. The 

 phosphorus of Romberg [really a pyrophore] burns also furiously upon 

 the approach of air. 



The last class, those which act after bei7ig exposed to the external 

 light, are exceedingly numerous; there seem but two substances which 

 do not emit light when tried in this way, water, in it's fluid state, and 

 metals. All bodies then, whatever, except water and metals, have a power 

 of imbibing light, and when placed in proper circumstances of emitting 

 it again. 



Adams was a firm believer in phlogiston and in the corpuscular 

 theory of light, treating it as a kind of matter. He wrote: 



Phosphoretic and phlogistic bodies agree in containing a quantity of 

 light, which is not in any perceived state of heat. 



Although phlogistic and phosplioretic bodies emit light upon the same 

 principles, so far as this depends upon luminous matter contained in 

 the bodies, which is set at liberty during the operation, by which it is 

 rendered luminous; yet the manner in which the luminous matter is set 

 at liberty, is very different, as is that also by which the luminous matter 

 is retained. The exposure to the atmosphere is essential to the emission 

 of light from phlogistic bodies; but this is a circumstance indifferent or 

 unnecessary for the same operation in those that are phosphoretic. In 

 phosphoretic bodies there is no difference perceived after they have lost 

 their shining qualities; but this is not the case with phlogistic bodies, 

 where the greatest difference is perceived on the abstraction of their 

 luminous matter. 



Phosplioretic bodies furnish us with a strong additional proof of a 

 principle already noticed, that light is matter which may continue for 

 some time therein without exciting heat, and may be again separated 

 therefrom, and resume it's character of light, . . . 



Such are the views on luminescence of selected writers of the 

 eighteenth century, views expressed in the hope of unifying ideas of 

 lisht, heat, fire, and flame in their various manifestations. 



Tracts mid Theses on Luminescence 



During the middle of the eighteenth century many observations 

 were made on sea luminescence, on electroluminescences in evacu- 

 ated vessels, and on phosphorescences, but few papers appeared of a 

 general nature, comparable to the earlier essays of de Mairan, 

 Cohausen, Dufay, or Beccari. This statement is particularly true in 

 the field of bioluminescence and contrasts strongly with the situa- 

 tion in the next century, when many general works on the light of 

 plants and animals were published. The eighteenth-century student 



