278 History of Luminescence 



moist effluvia, which very readily condense on the Glass, might, as near 

 as I could, be thrown off from every part of it,) by this means the Light 

 improv'd; and so continued to increase, till words in Capital Letters 

 became legible by it: (as has been observed by Spectators.) Nay, I have 

 found the Light produc'd to be so great, that a large Print might with- 

 out much difficulty be read by it: and at the same time, the Room, which 

 was large and wide, became sensibly enlightned, and the Wall was visible 

 at the remotest distance, which was at least 10 Foot. The Light was 

 of a curious Purple Colour, and was produc'd by a very slender touch 

 of the Hand; the Globe at the same time being scarce sensibly warm: 

 neither could I ever find, that a more violent Attrition did contribute 

 any thing to the increase of the Light. 



He then let in the air and noticed that when the globe was re- 

 volved no inner light appeared on touching, but that: 



For if a Man touch'd the Globe with his Fingers, there were specks of 

 Light (tho' without any great Lustre) seen to adhere to them. Nay, 

 while my Hand continued upon the Glass, (the Glass being in motion) 

 if any Person approach'd his Fingers towards any part of it in the same 

 Horizontal Plane with my Hand, a Light would be seen to stick to 'em, 

 at the distance of an inch or thereabouts, v^^ithout their touching the 

 Glass at all; as was confirm'd by several then present. 



Hauksbee next studied the appearances with different amounts 

 of air present in the globe and compared these effects with the dif- 

 ference in behaviour of mercury shaken in vacuo and in different 

 amounts of air. His globe experiments confirmed his view that the 

 mercurial light came not from any peculiarity of mercury but from 

 the rubbing of the mercury on the glass walls. 



Hauksbee then showed that attrition of a number of substances 

 in vacuo would result in a light. His device for doing this is illus- 

 trated in figure 24. When amber beads were rubbed against woolen 

 in vacuo a light appeared which " is not a meer lambent Fire, but 

 such as is accompanied by great Heat." He noted " That this Light 

 depends so immediately on the Attrition, as to disappear where it 

 ceases. That it requires a very thin and rare Medium, in order to 

 its Appearance: And the thinner the Medium, the greater the Ap- 

 pearance." The light was much greater in vacuo and was due of 

 course to an electric discharge at reduced pressure. 



Hauksbee also studied the light from attrition of various com- 

 binations in vacuo, flint and steel, glass on oyster shells (" a fierce 

 flaming of spark ") , oyster shells on woolen (" a dim one, and, at 

 best like a faint Halo ") , woolen on woolen (" a small glimmering 

 Light ") , glass on glass (" a considerable Light," the color " of 

 melted Glass ") . 



