704 PHILOSOPHICAL TRANSACTIONS. [aNNO 1763. 



produce no rarefaction of the air included in a tube. Which shows that the 

 wires are not heated by the fires passing through them. 



Exp. 8. When the wires are about 2 inches apart, the charge of a three- 

 pint bottle darting from one to the other, rarefies the air verj^ evidently. 

 Which shows that the electric fire must produce heat in itself, as well as in the 

 air, by its rapid motion. The charge of the case of bottles sent through the 

 brass wire consumed great part of it into smoke. The thermometer appeared 

 quite opaque with it. 



Exp. 9. He suspended a piece of brass wire, about 24 inches long, with a 

 pound weight at the lower end ; and, by sending the charge of the case of 

 bottles through it, discovered a new method of wire-drawing. The wire was 

 red hot, the whole length well anealed, and above an inch longer than before. 

 A 2d charge melted it ; it parted near the middle, and measured when the ends 

 were put together, 4 inches longer than at first. 



Exp. 10. That he might have no doubt of the wire*s being hot as well as 

 red, he repeated the experiment on another piece of the same wire, encompas- 

 sed with a goose-quill filled with loose grains of gunpowder ; which took fire as 

 readily as if it had been touched with a red hot poker. Also tinder, tied to 

 another piece of the wire, kindled by it. He tried a wire about twice as thick, 

 but could produce no such effects as that. Hence it appears, that the electric 

 fire, though it has no sensible heat when in a state of rest, will, by its violent 

 motion, and the resistance it meets with, produce heat in other bodies when 

 passing through them, provided they be small enough. A large quantity will 

 pass through a large wire without producing any sensible heat ; when the same 

 quantity passing through a very small one, being there confined to a narrower 

 passage, the- particles crowding closer together, and meeting with greater 

 resistance, will make it red hot, and even melt it. And hence lightning does 

 not melt metal by a cold fusion, as we formerly supposed. But when it passes 

 through the blade of a sword, if the quantity be not very great, it may heat the 

 point so as to melt it, wliile the broadest and thickest part may not be sensibly 

 warmer than before. And when trees or houses are set on fire by the dreadful 

 quantity which a cloud, or the earth sometimes discharges, must not the heat 

 by which the wood is first kindled, be generated by the lightning's violent 

 motion through the resisting combustible matter. 



Mr. K. then adds a dissertation, showing, from experience, the usefulness of 

 pointed conductors to houses, in securing them from a stroke of lightning. 



