202 History of Luminescence 



undue influence and personal prejudice at the beginning of the 

 nineteenth century. 



The essays of Link and Heinrich were published together in book 

 form in 1908 by the Royal Academy of Sciences at St. Petersburg 

 under the title Ueber die Natur des Lichts. Link's essay, " Ueber 

 die chemischen Eigenschaften des Lichts," of 92 pages, appears first 

 in the book. It was divided into four parts as follows: L Effects of 

 light; IL Effects of colored light; IIL The development of light 

 and IV. The relation of light to other bodies, matter, heat, and elec- 

 tricity. As winner of a prize, the essay is distinctly disappointing. 



A very short section dealt with phosphors (Lichtsaugende 

 Korper) , including as luminescences the light of phosphorus (also 

 the light of burning sulphur and arsenic) and the " lifeless but not 

 necessarily foul " luminescent organic bodies (wood or fish) . Link 

 considered the latter to be light magnets, i. e., the luminescence was 

 believed to result from insolation, chiefly because of the effect of 

 heat, which increased both the light of inorganic phosphors and of 

 the dead organic material. Link emphasized that the consistency of 

 the material was an important attribute of luminous bodies but 

 hesitated to propose a theory as to why one substance would lumi- 

 nesce and another not. Sea light along the north sea, channel, and 

 Atlantic coasts he attributed to small transparent jelly-like spheres, 

 1 line (%2 inch) in diameter, which looked like eggs and which he 

 thought to be eggs of medusae. They were undoubtedly Noctiluca. 



Heinrich Friedrich Link (1767-1851) was a physician and a pro- 

 fessor, first of natural history, chemistry, and botany at the Univer- 

 sity of Rostock, since 1811 professor of chemistry and botany at the 

 University of Breslau, and later (1815) professor of botany and 

 director of the botanical gardens at the University of Berlin. Link 

 was a voluminous writer on many diverse subjects, but it is as a 

 botanist that he is best known. 



PLACIDUS HEINRICH 



Heinrich's prize essay of 287 pages, Von der Natur und Eigen- 

 schaften des Lichts; Eine physisch-chemische Abhandlung (1808), 

 was divided into six parts, the first three dealing with the effects 

 of light on animals, plants, and chemical processes, respectively. The 

 fourth part was on luminescence and burning, sixty-six pages de- 

 voted entirely to various luminous phenomena. A fifth part was 

 concerned with the analysis of light by the prism, with " electric 

 light " and " galvanic light," and a sixth part with the properties 

 of light. In the latter Heinrich held that light was something that 



