40O PHILOSOPHICAL TRANSACTIONS. [aNNO I759. 



mained so for some time. In this state they were electrified minus ; for they 

 receded from the amber. 



Exp. 17. On bringing the finger near the convex side, the balls receded far- 

 ther from each other, as they did in the 13th experiment: and on repeating the 

 approach, the balls receded a little more, unless the stone was become too cold. 



Exp. 18. On removing the tourmalin the least from the wood, the balls ap- 

 proached nearer each other, and continued to do so as the stone was removed 

 farther off; yet they were electrified minus, though in a less degree. 



Exp. 19. He then removed it entirely, and the balls receded, but to a greater 

 distance than at any time before in the preceding experiments ; and instead of 

 being minus, they were now plus; for the amber caused them to apcede. 



Exp. 20. The tourmalin being again fixed to the wax, he gave the convex 

 side one slight rub with the finger, and observed that both sides were electrified 

 plus. When the tourmalin was put into its natural state, so as to electrify plus 

 and minus, he gave the same side another slight rub; and in this case both sides 

 were electrified plus. On repeating these last two experiments with the plain 

 side instead of the other, the tourmalin was electrified plus on both sides like- 

 wise; but with this diflference, that now they were considerably more electrified 

 than before. 



Exp. 21. To electrify glass minus, he made use of the same glass, and when 

 it was a little warmed as before, held it within 1 feet of the prime conductor, 

 which was electrified plus. By this method, that part of the glass, which was 

 opposed to the conductor, became electrified minus on both sides; but beyond 

 that a considerable part all round the minus, was electrified plus on both sides. 

 This effect is of the same kind with that mentioned in the 9th experiment. In 

 a few minutes, the minus electricity disappeared, and the plus continuing, dif- 

 fused itself into the place of the other; so that now the whole was electrified plus. 



Exp. 22. The experiment so far succeeding, induced him to make use of a 

 less piece of glass, that he might have the whole electrified minus. On making 

 the experiment, it answered accordingly. 



Exp. 23. He exposed the small piece of glass to the prime conductor, at the 

 distance of 2 feet, which was the same as before in the 2 1 st experiment, and 

 observed a minus electricity at both surfaces. 



Exp. 14. As he moved the glass nearer, to a certain distance, it was more 

 sensibly electrified minus; and after that, on moving it still nearer, the minus 

 appearance was less and less sensible, till it came within the distance of about 

 one inch, and then it was electrified plus on both sides. 



Exp. 25. This plus electricity in the glass he found might be changed to a 

 minus once again, by removing the glass, and holding it for a time at a greater 

 distance: which is another proof of the repulsive power of this fluid. 



