270 History of Luminescence 



ties, often referred to as Tracts on Magnetism; and Electricity 

 (1675). 



The term " electric virtue," universally used to describe the new 

 properties of electrified bodies, stems from Gilbert's idea of the orb 

 of virtue about a magnet, within which magnetic effects are detect- 

 able. There was also the orb of coition, within which small bodies 

 actually move toward the magnet. These orbs were spoken of as 

 " effused " and to have " effluent strengths." The electric effluvium 

 of amber was regarded as corporeal like a vapor given off from a 

 liquid.^^ Later, all sorts of properties and characteristics were re- 

 ferred to as virtues, especially by von Guericke, who spoke of the 

 " lighting virtue " and " coloring virtue " of the sun, of " sounding 

 virtue " when a sound was heard. It is no wonder that the electric 

 virtue and the lighting virtue or electric light and fire should be 

 regarded as the same thing by Wm. Watson as late as 1752. 



OTTO VON GUERICKE 



The invention about 1660 by Otto von Guericke (1602-1686) of 

 a device to generate electrical charges first called attention to the 

 " electric light," and indicated a connection between the electric 

 virtue and the lightning virtue. Von Guericke's machine was a ball 

 of sulphur which could be rotated on a shaft. It was charged by 

 holding the hand on it during rotation, and von Guericke (1672) 

 himself noticed that " if you take the globe with you into a dark 

 room and rub it, especially at night, light will result, as when sugar 

 is beaten." 



The review of von Guericke's book, Experimenta Nova Magde- 

 burgica (1672) , for the Royal Society ^^ emphasized the philosophi- 

 cal aspects of his discoveries rather than the electrical phenomena. 

 Von Guericke 



thinks may be represented the chief Vertues he enumerates of our Earth, 

 perform'd by a Globe of Sulphur melted and cooled again, and then 

 perforated to traject an Iron axis through it for circumvolution; whereby 

 attrition being used withall, he affirms that the Impulsive, Attractive, 

 Expulsive and other vertues of the Earth, as he calls them, may be 

 ocularly exhibited. 



Von Guericke's globe possessed not only the virtue of light but 

 also a virtue of sound, " for when it is carried in the hand or is 

 held in a warm hand and thus brought to the ear, roarings and 

 cracking are heard in it." It was in fact an electric terella instead of 



^^ See R. Boyle, Essays of effluviums, etc., London, 1673. 

 »'Phil. Trans. (No. 88), 5103-5105, 1672. 



