A HISTORY OF SCIENCE 



tribute much to electricity, but three experiments con- 

 vinced me to the contrary. The first, that by warm- 

 ing the pieces of gauze neither the black nor white 

 pieces obstructed the action of the electrical tube more 

 than those of the other colors. In like manner, the 

 ribbons being warmed, the black and white are not 

 more strongly attracted than the rest. The second is, 

 the gauzes and ribbons being wetted, the ribbons are 

 all attracted equally, and all the pieces of gauze equal- 

 ly intercept the action of electric bodies. The third 

 is, that the colors of a prism being thrown on a 

 white gauze, there appear no differences of attraction. 

 Whence it proceeds that this difference proceeds, not 

 from the color, as a color, but from the substances that 

 are employed in the dyeing. For when I colored rib- 

 bons by rubbing them with charcoal, carmine, and 

 such other substances, the differences no longer proved 

 the same." 



In connection with his experiments with his thread 

 suspended on glass poles, Dufay noted that a certain 

 amount of the current is lost, being given off to the sur- 

 rounding air. He recommended, therefore, that the 

 cords experimented with be wrapped with some non- 

 conductor that it should be "insulated" ("isolee"), 

 as he said, first making use of this term. 



Dufay Discovers Vitreous and Resinous Electricity 



It has been shown in an earlier chapter how Von 

 Guericke discovered that light substances like feathers, 

 after being attracted to the sulphur-ball electric- 

 machine, were repelled by it until they touched some 

 object. Von Guericke noted this, but failed to ex- 



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