198 History of Luminescence 



Inorganic phosphors and luminous organisms thus came within 

 the sphere of Davy's interest but it must be emphasized that the 

 above quotations represent his early views. The material nature of 

 light, which assumed the ability to combine with matter, was a 

 generally accepted belief at that time, a continuation of eighteenth- 

 century thought. 



THOMAS YOUNG 



In 1804 * the material theory of light was seriously questioned by 

 Thomas Young, M. D. (1773-1829), whose studies on diffraction 

 and interference completely supported a wave theory. Young was a 

 man of unusual talents and broad interests, not only a physician and 

 physicist, a student of both physical and physiological optics, and a 

 mathematician, but also a linguist and Egyptologist. He was For- 

 eign Secretary of the Royal Society and Professor at the Royal Insti- 

 tution. In his two-volume Course of Lectures on Natural Philoso- 

 phy and the Mechanical Arts (1807) , Young elaborated on his inter- 

 ference theory and touched on luminescences. He used Lavoisier's 

 word " oxygen," stating that light and heat from terrestrial sources 

 mostly came from combustion, which 



is not capable of a very correct definition: in general it requires an 

 absorption, or at least a transfer, of a portion of oxygen; but there appear 

 to be some exceptions to the universality of this distinction; and it has 

 been observed that both heat and light are often produced where no 

 transfer of oxygen takes place, and sometimes by the effect of a mixture 

 which cannot be called combustion. 



Light is also afforded, without any sensible heat, by a number of 

 vegetable and animal substances, which appear to be undergoing a slow 

 decomposition, not wholly unlike combustion. Thus decayed wood, and 

 animal substances slightly salted, often afford spontaneously a faint liglit, 

 without any elevation of temperature; and it is not improbable tliat the 

 light of the ignis fatuus may proceed from a vapour of a similar nature. 



He also described the solar phosphori and luminous phenomena, 

 " attributed to the motions of the electrical fluid," but he merely 

 mentioned the general facts without interpretation. In a section 

 entitled, " Catalogue of Works Relating to Natural Philosophy," 

 there is a surprisingly complete subject bibliography ^ with some 



* See the Bakerian Lecture of T. Young, " Experiments and calculations relative to 

 physical optics," Phil. Trans. 94: 1-16, 1804. 



^ Special subject bibliographies on luminescence started at the end of the eighteenth 

 century with Joseph Banks (1743-1820) , Catalogus bibliothecae historico-naturalis, 

 which appeared from 1796-1799 in four volumes— I Scriptores generales, II Zoologi, 

 III Botanici, IV Mineralogi. In the zoology volume a section on Phosphorescentia 

 animalium and Phosphorescentia maris contains thirty-eight references. In the volume 



