Electroluminescence 279 



The glass on glass experiment was even tested under water when 

 " A pretty brisk Light was produc'd," red in color, but the most 

 important observations came from the attrition of glass and woolen. 

 In vacuo this " quickly produc'd a beautiful Phenomenon, viz, a 

 fine purple Light, and vivid to that degree, that all the included 

 Apparatus was easily and distinctly discernable by the help of it. 

 And thus it continued while the friction lasted." 



If the woolen cloth was soaked in spirit of wine or impregnated 

 with saltpetre " I observ'd the Light to break from the agitated Glass 

 in a very odd form, resembling that of Lightning. This is mani- 

 festly different from the last Phenomenon: For there indeed we had 

 a delicate Purple-colour d Light; but here, a brisk fulgurating Light, 

 scattering itself about in Flashes, and darting with a force from the 

 surface of the revolving Glass." 



Hauksbee realized that rubbing the glass electrified it so that 

 brass foil and threads were attracted, and that both noise and light 

 were apparent. In one experiment a bright light appeared inside 

 an exhausted glass globe which was arranged within a rotating glass 

 globe filled with air (see fig. 24) . When rotation stopped the light 

 disappeared but returned when rotation was again started. If both 

 globes were rotated the light was much brighter. If the hand was 

 brought " near the surface of the outer Glass, there would be Flashes 

 of Light (like Lightning) produc'd in the inward Glass; just as if 

 the Effluvia from the outer glass, had been push'd with more force 

 upon it by means of the approaching Hand." 



Hauksbee was particularly interested in the relation between 

 electrical and luminous effluvia and cited a number of cases which 

 finally led him to declare that there was " a real difference ... (at 

 least in some Cases) " between the two. " For these Qualities re- 

 quire different Circumstances with respect to the Circumjacent 

 Medium, in order to their discovering themselves." His researches 

 on electrical discharge in vacuo were so varied and so significant as 

 to establish him as the true discoverer of electroluminescence in the 

 laboratory; nor should it be forgotten that he was the inventor of 

 an electrical machine in use for half a century. 



Hauksbee's experiments may be said to have set the scientific 

 world to rubbing and it soon became evident that rubbing various 

 materials would quite regularly result in a luminescence, whether 

 in a vacuum or in the air. A statement in the Histoire of the French 

 Academy (see Martyn and Chambers 3: 3-5, 1742) for 1707 referred 

 to the new " perpetual phosphorus " of Johann Bernoulli, " which 

 could not fail of raising the curiosity of philosophers, and especially 

 those of the academy, who had a sort of right to a discovery made 



