84 Mr. J. J. Waterston on some Electrical 



made in the coating of the knob (the outside of jar being pre- 

 viously touched) ; the plate, held as before, obtained a charge of 

 the same electricity as the knob. 



c. The plate held with its edge to the completely coated knob 

 obtained a charge of the same electricity as the knob. 



d. The plate held as in c } but with edge covered with wax, 

 received no charge. 



In these experiments the insulation of the plate must be very 

 perfect. The only way found to answer was suspending the 

 plate by a flat ribbon of the finest shell lac, heated, and drawn 

 out strong enough, when cool, to withstand the disposition of such 

 plates to turn end on to the acting surface. 



6. e. A cake of lac was substituted for the metallic plate in 5 b, 

 and, like the plate, the cake obtained a charge of same electricity 

 as the knob. 



/. Experiment 5 c was repeated with the cake, and the effect 

 was a slow gradual charge of electricity different from that of the 

 knob ; i. e. the knob being positive, the cake becomes slowly and 

 gradually negative. 



g. The knob of the jar being touched and the lac cake held 

 with its face close to the coated outside of the jar (which teemed 

 with electricity), it received no immediate charge of same elec- 

 tricity as outside coating, but slowly and gradually it received a 

 charge of the opposite electricity. 



h. The same cake held close to the bottom angle outside of 

 jar opposite a part uncovered with wax, receives an immediate 

 charge of same electricity as outer coating. 



Note. To remove electrical excitement from shell lac and cakes 

 of non-conducting matter, two small flames were employed, one 

 on each side, simultaneously. 



7. The prime conductor of an electrical machine, when hot 

 (cylinder 10 inches in diameter), was coated with shell lac. 

 When cold and the coating hard, the machine was put in action 

 and a blunt wire held near the coated conductor (brass cylinder 

 15 inches by 3 inches). Brushes were projected from the wire 

 to the coated conductor, and luminous points appeared left by 

 the brush and, as it were, imbedded in the shell lac. To con- 

 tinue to give brushes, it was necessary to remove the wire oppo- 

 site to parts where these luminous points had not yet appeared. 



8. a. On taking sparks from this shell-lac-coated prime con- 

 ductor, each spark makes a hole in the coating ; and if we do 

 not hold the ball exactly^opposite one of these holes, the electric 

 fire takes an angular course, describing the perpendicular to the 

 surface of the prime conductor, and then along the surface of 

 the lac to the nearest hole (Plate II. fig. 1). 



h. A thin piece of orange lac in the shell s s (fig. 2), having a 



