558 I'HILOSOPHICAL TRANSACTIONS. [aNNO 1774. 



The use of the Glass Conductor. — ^The glass tube, thus furnished and mounted, 

 being properly exhausted, and perfectly dry, will act in all respects like one of 

 metal ; and the electrometer, being placed on the brass ball b, will answer 

 exactly to the charge of a jar or battery. But the principal use of this instru- 

 ment, is to ascertain the direction of the electric matter, as it passes through it. 

 And this end it completely answers in the manner following, viz. set it with the 

 collecting point f, before the globe, and place the knob of an uncharged bottle 

 nearly in contact with the brass ball b, or hang a chain, &c. from it to the table; 

 and, on working the machine, the ball d in the tube becomes entirely enveloped 

 in a dense white atmosphere of electricity. If the point f be brought nearly 

 into contact with an insulated rubber, and a communication be made from the 

 ball B to the table ; the atmosphere will be on the ball e in the tube. If a 

 bottle, positively charged, be presented as in the drawing, fig. 18, the appear- 

 ances in the tube will be as there delineated. But if a bottle charged negatively, 

 be thus applied, the atmosphere will surround the ball e in the tube, as in 



fig- 19- 



If, instead of the brass balls in the tube, points are used ; or if a point be 



fixed at one end of the tube, and a ball at the other, the effect will be precisely 

 the same. — Note also, that the glass conductor, for the purpose of making Dr. 

 Franklin's curious experiments, with a pointed and blunted wire, is far superior 

 to one of metal, the electric atmosphere being so much better retained by it. 

 By this easy and simple process, may an ocular demonstration, at all times, be 

 given, in a dark room and dry air, of the truth and propriety of Dr. Franklin s 

 hypothesis of the Leyden bottle. 



§ 5. Miscellaneous Experiments, made principally in the Years 1771 arid 1772. 

 ■ ' Exper. 1. If a black silk ribband, or a piece of black silk, be laid on a quire 

 of paper, &c. on a table, and excited by drawing over its surface sealing-wax, 

 sulphur, amber, or a tube of glass with the polish taken off by emery, its elec- 

 tricity will be positive : whereas, if it be excited singly, or together with a white 

 ribband, by drawing them briskly between the fingers it is always negative. 

 Laying it on the paper, and drawing over its surface a rod, or tube of smooth 

 glass, its electricity will also be negative. 



Exper. 1. If a plate of glass, 10 or 12 inches in diameter, be excited, and 

 placed on the top of a box, from which a pair of light pith or cork balls are sus- 

 pended, being mounted on a stand of sealing-wax ; the balls will separate, and 

 stand repelled from each other, being electrified positively, in a dry air, upwards 

 of 4 hours. When they come into contact, on removing the glass, they di- 

 verge again, and are negatively electrified ; but on replacing it they close. On 

 removing it again they separate ; and thus alternately as long as any electricity 

 remains in it. 



