94 History of Luminescence 



seem to be of the same nature with shining wood: and it is true, that 

 all putrefaction hath with it an inward motion, as well as fire or light. 



Bacon showed great intuition by recognizing the essential simi- 

 larity of the light from shining wood, due to fungal mycelia, and 

 the scales of fish, now known to be due to luminous bacteria. He 

 paid scant attention to the nature of light itself and in fact com- 

 plained " that the form and origin of light had been but little 

 inquired into," that rays of light had been considered only mathe- 

 matically with little attention paid to them physically. " This there- 

 fore he placed among the desiderata of his time, and desires that 

 inquiry may be made into it." ^ 



The Bolognian Stone and Phosphorescence 



Another great scientist at the beginning of the seventeenth cen- 

 tury, Galileo Galilei (1564-1642) , was also interested in light, but 

 was concerned more with that from heavenly bodies than with the 

 variety found on earth. There appears to be no discussion of the 

 firefly or of shining wood in Galileo's writings, but he was one of the 

 first to become acquainted with the Bolognian stone or Bolognian 

 phosphor, perhaps the greatest discovery in the entire history of 

 inorganic luminescence. Galileo demonstrated to La Galla (1612), 

 who first published the account, how the material after exposure to 

 daylight would light in the dark. This phosphor exemplified a new 

 method of light production, now specifically spoken of as phos- 

 phorescence. Since phosphorescence is merely a delayed fluores- 

 cence, it is no exaggeration to claim that the Bolognian phosphor, 

 after more than three hundred years, through invention of the 

 fluorescent lamp, finally revolutionized the lighting industry and 

 made the development of television possible. 



The Bolognian or Bononian phosphor or phosphorus was first 

 prepared by an Italian shoemaker of Bologna, Vincenzo Cascariolo, 

 a dabbler in alchemy. In 1603 he found that a local stone, now 

 known as heavy spar, a native barium sulphate, after special treat- 

 ment by calcination, would " imbibe " the light of day and emit it 

 later in the dark. The material aroused the greatest interest among 

 the learned of the time, and led to a famous controversy between 

 Galileo and Liceti concerning the light of the moon. A detailed 

 history of the discovery of the stone and an account of the work of 

 many subsequent investigators who studied the Bolognian and simi- 

 lar phosphors, will be described in Chapter VIII on Phosphorescence. 

 It is sufficient to emphasize here that the storage of light, an entirely 



8 Quotations from Priestley (1772: 43-44) . 



