Image from page 461 of "The principles of physics" (1895)
Title: The principles of physics
Publisher: Boston, London, Ginn
Contributing Library: Cornell University Library
Digitizing Sponsor: MSN
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ass tumblers, used as legs. Let a person, whom we willcall John, stand on this stool, and hold in one hand one end of a wire(say) 4 yds. long, the other end of which is attached to the disk of an electroscope, a. Let asecond person, James,strike John with a catsfur; the leaves diverge.6. Substitute a white silkthread for the wire, touchthe electroscope with afinger so as to dischargeit, and repeat the last op-eration ; the leaves do notdiverge, c. Let Jamesstrike John several timeswith the fur, and thenbring a finger knucklenear to some part ofJohns person, e.g. thechin, nose, or a knuckle(Fig. 336); an electric spark will pass between the two and both willexperience a slight shock. The electricity which had accumulated onJohn in consequence of his insulation, escapes or is discharged throughJames. > If the air were a conductor of electricity, a body could not be cliargad in it;there could be no thunder storms, and man would probably never have known of theexistence of electricity.
Text Appearing After Image:
Fig. 336. ELECTRICITY ACTS ACROSS A DIELECTRIC. 441 Section II. INDUCTION. 401. Electricity acts across a dielectric. Experiment 1. —Fig. 337 represents an empty egg-shell covered withtin foil to make it a good conductor. It is suspended from a glass rodby a silk thread, a. Electrify aglass rod and bring it near theshell. The shell moves toward therod. 6. Next introduce a glassplate between the rod and shell.The shell approaches the rod asbefore. The chief lesson we learnfrom this experiment is thatelectricity acts across a dielec-tric} In a the dielectric wasair ; in b, air and glass. 402. To determine what ac-tually happens on an insulatedconductor when an electrifiedbody is brought near. ^^^- ^^• Experiment 2. — a. Suspend, as above, two shells so as to touch eachother, end to end, as in Fig. 338, thus making practically one conductor.Bring near to one end of tlie shells a sealing-wax rod, D, excited with—E. While the rod is in this position carry a thin strip of tissue pap
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