104 Experimental Philosophy. [Lecture 8. 



covered or smeared over with what is called an 

 amalgam^ or a mixture of tin and mercury. A 

 small chain is also annexed to the apparatus, in 

 order to make a communication with the earth ; 

 which is always necessary, as the electrical fluid 

 is all supposed to be ultimately derived from the 

 earth. When the chain is laid over that con- 

 ductor which communicates with the cushion, 

 then that conductor is no longer insulated, but 

 an immediate communication is established with 

 the earth : if, on the contrary, the chain is taken 

 from it, and laid over the prime conductor, dif- 

 ferent effects are produced, which we shall en- 

 deavour hereafter to explain. 



It is scarcely necessary to add that the elec- 

 trical power is excited by turning the cylinder 

 pretty quickly round, while it rubs against the 

 cushion. On turning the cylinder for a little 

 time in this manner, we find that sparks may be 

 drawn by the knuckle from the prime conductor, 

 which is then charged or loaded with the electric 

 matter, and this matter has a kind of sulphureous 

 smell. Again, if a metallic plate is placed at 

 some distance beneath the conductor, and some 

 light bodies, such as feathers, straws, or little 

 images of men and women cut in paper are pre- 

 sented to it, they will be first attracted to the 

 conductor, they then become in effect conductors 

 themselves, and, as soon as charged with the 

 electrical matter, they will be repelled; they will 

 then fly to the plate, and discharge the electricity 



