474 l-HILOSOPHICAL TRANSACTIONS. [aNNO 1778. 



motion, and will continue so for some seconds. When their motion ceases, 

 withdraw the amber, &c. and the motion of the filings will be renewed, and 

 continue as at first ; this shows, that in both cases, they really act as conductors 

 of the electric fluid between the lower surface of the glass and the bottom of 

 the box, in order to restore an equilibrium, as on Dr. Faanklin's principles they 

 ought to do ; and that the electric fluid does not, like the magnetic, absolutely 

 permeate the glass. 



Exper. — Take a clean, dry, thin jihial, about 4 inches long, and 1 inch in 

 diameter. In the cork of this phial fix a small loop of very fine iron wire. In 

 the loop suspend another wire, about 24- inches in length, by a similar loop ; 

 and on the lower end hang a light round ball of the pith of elder or cork, and 

 be careful to give the wire as free a motion as possible. Let one of the ends of 

 a small magnetic bar be brought near the side of the phial, then the little ball 

 will instantly come to the glass, and there remain as long as the magnet is held 

 within the distance of its influence. Remove the magnet, and the ball instantly 

 retires to, and remains in the centre of the phial : then dry and warm the glass, 

 and let an electric strongly excited be applied to the side of the phial, as the 

 magnet was in the former experiment ; the ball instantly comes to the side of 

 the glass, and there remains some seconds, and then returns to the centre of the 

 phial. Withdraw now the excited electric, and the ball instantly returns to the 

 glass on the principle before-mentioned, which is more completely shown by the 

 filings in the little box. 



£xper. — Let a piece of thin glass be placed as a cover to a circular box, about 

 6 inches in diameter, and \ of an inch deep : put into the box 20 or 30 light 

 balls of cork, or of the pith of elder ; then, having made the glass very dry and 

 warm, expose its surface to the electric matter issuing from the prime conductor 

 to a good electrical machine ; the balls will be instantly in motion, and will so 

 continue for some time, the box being moved in such manner that every part of 

 the glass may be affected. Th.en remove the box, and the balls being at rest, 

 turn the glass, placing the upper surface downwards ; the balls will then instantly 

 renew their motion. When this 2d motion ceases, touch the surface of the 

 glass near the centre with a finger, or, which is better, with a round, smooth 

 piece of wood or metal, the balls will instantly fly to either of these, and will 

 frequently pile themselves up between the glass and the bottom of the box, 8 or 

 10 in a pile, and will remove themselves, following the wood, &c. to different 

 parts of the glass, till the charge is exhausted. Apply the glass again to the 

 conductor as before, and when the motion of the balls nearly ceases, remove 

 the glass, and place on each surface a circular coating of metal, reaching within 

 an inch of the edge of the glass all round. Make a communication between 

 these coatings, and the glass will then show that it has been charged, and will 



