A HISTORY OF SCIENCE 



long, I cut the great end of it to fit into the bore of the 

 tube, into which it went about five inches ; then when 

 the cane was put into the end of the tube, and this ex- 

 cited, the cane drew the leaf -brass to the height of 

 more than two inches, as did also the ivory ball, when 

 by a cork and stick it had been fixed to the end of the 

 cane. . . . With several pieces of Spanish cane and fir- 

 sticks I afterwards made a rod, which, together with 

 the tube, was somewhat more than eighteen feet long, 

 which was the greatest length I could conveniently use 

 in my chamber, and found the attraction very nearly, 

 if not altogether, as strong as when the ball was placed 

 on the shorter rods." 



This experiment exhausted the capacity of his small 

 room, but on going to the country a little later he was 

 able to continue his experiments. " To a pole of eigh- 

 teen feet there was tied a line of thirty-four feet in 

 length, so that the pole and line together were fifty- 

 two feet. With the pole and tube I stood in the bal- 

 cony, the assistant below in the court, where he held 

 the board with the leaf -brass on it. Then the tube be- 

 ing excited, as usual, the electric virtue passed from the 

 tube up the pole and down the line to the ivory ball, 

 which attracted the leaf-brass, and as the ball passed 

 over it in its vibrations the leaf -brass would follow it 

 till it was carried off the board." 



Gray next attempted to send the electricity over 

 a line suspended horizontally. To do this he suspend- 

 ed the pack - thread by pieces of string looped over 

 nails driven into beams for that purpose. But when 

 thus suspended he found that the ivory ball no longer 

 excited the leaf -brass, and he guessed correctly that 



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