CATALOGUE. ELECTRICITY. 



421 



Erman on conducting powers. Gilb. XII 

 143. 



Shows that ice is a nonconductor. 



A thread of gum lac insulates ten times as well as silk. 

 A needle of sealing wax retains for some days its electric 

 polarity. A capillary bore lessens the insulating power of 

 glass. According to Saussure's hygrometer, the dissipation 

 of electricity by the air is nearly in the triplicate ratio of 

 its moisture. A jar will be discharged if sounded like a 

 harmonica. Robison. 



Table of Conductors, in order, chiefly from 

 Cavallo. 



Conduclors. 

 Gold. 

 Silver. 

 Copper. 

 Platina. 

 Brass. 

 Iron. 

 Tin. 



Mercury. 

 Lead. 



Semimetais. 

 Metallic ores. 

 Charcoal. 

 Animal fluids. 

 Acids. 



Saline solutions. 

 Hot water. 

 Cold water. 



Liquids, excepting oils. 

 Red hot glass. 

 Melted resin. 

 Flame. 

 ~Ice, not too cold. 

 Metallic salts. 

 Salts in general. 

 Earths and soft stones. 

 Glass, filled with boiling 



water. 

 Smoke. 



Steam or vapour. 

 An imperfect vacuum. 



Hot air. 



In Henley's experiments, the 

 same charge melted of gold 

 wire 4 inches, of brass 6, of 

 silvered copper 8, of silver lo, 

 of iron lo or more. Copper 

 is allowed to conduct much 

 more readily than irotj. Nairne. 

 Platina is said by some to be 

 a bad conductor. 



Seems to be placed too low. 



Snow. Cotte. 



Kinnersley. 



Yet the electrical machine works 



in a vacuum. 

 Read denies that hot air is a 



conductor. 



Nonconductors. 

 Ice, at — 13° F. Achard. 

 Powders, not metallic. Delaval. 

 Soft stones, when heated. Delaval. 

 Hard stones. 

 Dry vegetable substances. 



Baked wood requires to be 

 varnished. 



Ashes. 



Dry and complete oxids. 



Oils. 



Common air, and other gases. 



White sugar and sugar candy. 



Paper. 



Dry and external animal sub- 

 stances, as feathers, wool, 

 and hair. 



Cotton. 



Silk. 



Wax. 



Resins. 



Sulfur. 



Amber. 



Transparent gems. 



Glasi of all kinds. 



A pel feet vacuum. Morgan. 



White hair conducts less 

 perfectly than black. 

 __ Henley. Ph. tr. 1770. 



Glass often heated is best fSr 

 electrical purposes. Bosc, 



Motions of the Electric Fluid. Velocity. 

 Watson. Pli. tr. 1748. XLV.49, 491. 



No perceptible time was occupied in a circuit of 12273 

 feet : but the report was not so loud when the circuit was 

 so much extended. 



Simple Communication. 

 Nairne. Ph. tr. 1774. 79. 



Observes, that a ball was struck at the distance of nine 

 inches by the same charge that reached a point oply at six. 

 Perhaps, however, the point had very rapidly diminished 

 the charge. 



On the direction of the electric current. 

 Henley, Ph. Ir. 1774. 389. ii. 

 Flame is driven by a weak charge towards the negative 

 side. 



Henley on the long continuance of exci- 

 tation. Ph. tr. 1777. 85. 



