Electroluminescence 277 



very surprising manner." Some of the mercury globules rolled down 

 the sides of the glass and others fell directly and Hauksbee observed 

 that only the former, with a rotary motion produced light. Using 

 his mercury gage, he determined that only when the mercury was 

 sinking in the gage did light appear and only if the pressure was 

 about half an atmosphere or less. By allowing mercury to fall into a 

 vacuum and strike a rounded glass surface, Hauksbee noticed that 

 " the mercury did not only appear as a shower of Fire, but from 

 the Crown of the included glass were darted frequently Flashes re- 

 sembling Lightning of a very pale Colour, very distinguishable from 

 the rest of the Light produc'd." The two essentials for the appear- 

 ance of light from mercury appeared to be a rolling motion of the 

 mercury and a partially evacuated space. 



The latter requirement, however, was only necessary for the 

 brightest light. When the mercury was violently shaken in a globe 

 containing air at atmospheric pressure " Particles of Light appear'd 

 plentifully, about the bigness of small pin beads, very vivid, re- 

 sembling bright twinkling stars. ..." When the same vessel was 

 exhausted, " the mercury then did appear Luminous all round, not 

 as before, like little bright sparks, but as a Continued Circle of Light 

 during that motion." 



In a more modern version of the mercurial phosphor, a tube con- 

 taining mercury is filled with neon at low pressure. Because of the 

 low excitation potential and red luminescence of neon, it is easy to 

 observe that as the mercury is made to roll over the glass surface a 

 bright red glow appears at the rear end of the mercury drop as it 

 separates from the glass. By shaking the tube violently a beautiful 

 red glow can be obtained. These tubes are sometimes made in the 

 form of annuli and worn as earrings, which luminesce with every 

 turn of the head. 



Hauksbee's researches on light from mercury in glass vessels, which 

 he attributed to friction on the glass walls, led him to investigate 

 the effects of rubbing other materials. His first paper on the subject 

 in 1706 was entitled: "An experiment touching the production of 

 a considerable light upon a slight attrition of the hands on a glass 

 globe exhausted of its air; with other remarkable occurrences." 



This contribution presents the first experiments on electrolumi- 

 nescence following observation of the barometer light. The ex- 

 hausted glass globe was about nine inches in diameter, fixed on his 

 device for rotation: 



and then applying my naked Hand (expanded) to the surface of it, the 

 result was. That in a very little time a considerable Light was pro- 

 duc'd. And as I mov'd my hand from one place to another (that the 



