398 ' PHILOSOPHICAL TRANSACTIONS. [aNNO 175Q. 



Stone was colder, these appearances were considerably stronger ; but on cooling 

 still more they were less and less. 



Exp. 2. He repeated this last experiment, with the difference only of having 

 the balls electrified minus instead of plus.* And in this case (as might be ex- 

 pected) the effects were reversed; the balls acceding towards the convex side, 

 and receding from the plain side. 



Exp. 3. He presented the convex side to the flame of a candle, but not so 

 near as to touch the flame, and held it there about one minute, during which 

 time the stone acquired a plus electricity on both sides, for the balls receded 

 from them, but rather with a greater force from the convex side, than from the 

 plain side. 



Exp. 4. After a short time, the tourmalin being colder, and the remaining 

 heat more equally diffused, it changed its last state to a plus and minus one ; for 

 the plain side made the balls accede, and the convex side made them recede. 



Exp. 5. He now held the plain side as near the flame as he had done the 

 convex one ; and instead of both sides being electrified plus, they were electri- 

 fied minus, for each side caused the balls to accede. 



Exp. 6. After the same length of time as in the fourth experiment, the tour- 

 malin being colder, it changed its state also ; for the convex side made the balls 

 recede, and the plain side continued to make them accede, as they had done 

 before. He was naturally led next to examine at which surface of the tourmalin 

 the fluid entered (if any did), while it continued heating. 



Exp. 7- Flame being improper for the purpose, because the electric fluid is 

 readily dissipated by its presence, he made choice of an iron rod, at the end of 

 which was a round knob. This was heated, and afterwards brought to a certain 

 distance from the balls, in order to see if they were moved by it : but not per- 

 ceiving the least motion, he interposed the tourmalin, with the convex side next 

 the balls. They acceded a little, and when he removed the heated iron, they 

 returned to their place again. He then brought the iron nearer to the tourmalin 

 than before : the balls in this case moved with vigour towards the stone, and 

 continued in contact with it for a considerable time ; and after that they receded 

 from it. On examining the balls they had lost all their plus electricity, and were 

 electrified minus. He also observed that the stone itself was minus on both 

 sides. He gathered from this experiment, that the electric fluid flowed from 

 the balls towards the stone; because they not only lost their own plus electricity, 

 but were electrified minus ; and as the tourmalin was minus also on both sides, a 

 quantity of electric fluid must have flowed from it towards the iron. 



* He did the same thing in every ex|)eriment where there was occasion to use these balls, to be 

 more certain of the conclusions.— Orig. 



