216 History of Luminescence 



cence. This special treatment has been covered in the chapters deal- 

 ing with these three subjects. 



THE BECQUEREL FAMILY 



Because of their notable interest in luminescences, the various 

 texts of the Becquerel family, father and son, deserve special men- 

 tion. These began to appear about the same time as Gmelin's 

 chemistry, and may serve to clarify the point of view of the physicist. 

 One fact was becoming clear, that less and less attention would be 

 paid by physicists to the luminescence of " organized bodies," al- 

 though this type of light was still included in physics textbooks. 



Study of inorganic luminescences during the mid-century may be 

 considered the specialty of Edmond Becquerel (1820-1891) , pro- 

 fessor of physics at the Conservatoire des Arts et Metiers in Paris, 

 working in the fields of electricity and optics. Edmond Becquerel 

 was a real leader who made innumerable contributions to knowledge 

 of phosphorescence and fluorescence. He is perhaps best known for 

 spectral studies of the exciting and the emitted light, and as the in- 

 ventor of the phosphorescope by which short-lived phosphorescences 

 can be detected and their duration measured. His father, Antoine 

 Cesar Becquerel (1788-1878) , was an engineer and physicist, who 

 also studied (1826, 1839) phosphorescence, but is better known for 

 books on electricity and magnetism. Edmond's son, Henri Becquerel 

 (1852-1908) , was the discoverer of the radioactivity of uranium com- 

 pounds (1896) , and a student of phosphors and infrared light. 



One of the important works of the father, A, C. Becquerel (1788- 

 1878) , was the Traite Experimental de I'Electricite et du Mag- 

 netisme, a seven-volume work published in 1834-1840. In Volume 4, 

 Book 8 (54 pages) is entitled " De la Phosphorescence." The sub- 

 ject is divided into I " Principes generaux "; 11 " Les different modes 

 de phosphorescence "; III " Les causes qui influent sur la phos- 

 phorescence en general "; IV " De la phosphorescence des corps 

 organises et de la mer." Practically the same material is presented 

 in his two-volume Traite de Physique Consideree dans ses Rap- 

 ports avec la Chimie et les Sciences Naturelles (1842-1844) . The 

 first eight pages of the section, " De la Phosphorescence," are devoted 

 to bioluminescences under the headings " Phosphorescence spon- 

 tanee " (fish, meat, wood, and molluscs) , " De la phosphorescence 

 de les lampyres " and " Phosphorescence de la mer "; the remainder 

 deal with luminescence from rubbing, percussion, light exposure, 

 heat and chemical action. 



In connection with sea luminescence, Becquerel thought the light 



