VOL. LI.] PHILOSOPHICAL TRANSACTIONS. SQQ 



Exp. 8. When he heated the convex side in the same manner as he did the 

 plain one, the balls were not movtd towards the tourmalin, but from it, and 

 continued in that state. In this experiment they were electrified plus, and the 

 stone also was plus on both sides. 



Ejcp. g. When the plain side of the tourmalin was exposed to the heated end 

 of the glass, in like manner as it was to the knob of iron in the 7 th experiment, 

 he observed that about 3 inches of the heated part of the glass was electrified 

 minus, and beyond that distance it was electrified plus, and continued so even 

 when the glass was very nearly cold. 



Exp. 10. He was now eager to try what would be the event, when the heated 

 part of the glass was next the convex side of the tourmalin. On making the ex- 

 periment he found that the tube was electrified minus above one foot in length, 

 without the least appearance of a plus electricity beyond the minus one, as in the 

 last experiment. And this minus appearance confirmed also when the tube was 

 nearly cold. Now because the tourmalin was plus, the balls plus also, and the 

 heated glass minus, the electric fluid must have flowed from the glass to produce 

 a plus electricity in the stone and balls. 

 — His next step was to put the tourmalin into its natural state (as ^pinus calls 

 it), in order to make further experiments. 



Exp. 11. For this purpose he separated the tourmalin from the wax, and 

 placed it in boiling water for a short time, where it was surrounded on all sides 

 ' with a conductor and an equal degree of heat : then taking it out of the water, 

 he laid the convex side (after it was dry) on the slip of wood, supported by wax, 

 to which the pith balls were suspended; but no appearance happened, for the 

 balls continued at rest. 



Exp. 1 2. But when the stone remained on the wood a little time longer, the 

 balls separated to a considerable distance, sometimes near 2 inches; and remained 

 so for more than one minute. 



Exp. 13. If while the stone continued resting on the wood, he brought his 

 finger near the plain side of the tourmalin, the balls receded farther from each 

 other; and when he repeated the approach, it every time affected the balls and 

 made them recede a little more, unless the tourmalin was become too cold; in 

 which case they approached nearer, but still continued to be electrified plus. 



Exp. 14. On removing the stone by degrees from off the wood, the balls ap- 

 proached nearer and nearer : but when it was taken away entirely they receded 

 again, and in this case were electrified minus instead of plus. 



Exp. 15. After heating the stone again in boiling water, he laid the plain side 

 on the wood. In this case the balls continued at rest as they did in exp. 11, 

 when the convex side laid upon the wood. 



Exp. l6. But after a little time the balls separated an inch or more, and re- 



