306 



LESSONS IN ELECTRICITY. 



by a great electrician named ^Epinns. I 

 wish you to make these historic experi- 

 ments. Insulate an elongated metal con- 

 ductor, c c', fig. 21, or one formed of 

 wood coated with tin-foil even a carrot, 

 cucumber, or parsnip, so that it be insu- 

 lated, will answer. Let a small weight, 

 W, suspended from a silk string, s, re^t 

 en one end of the conductor, and hold 



FLO. 2L 



your rubbed glass tube, R, over the other 

 end. You can predict beforehand what 

 will occur when you remove the weight. 

 It carries away with it electricity, which 

 repels rubbed glass, and attracts your 

 balanced lath. 



Stand on an insulating stool ; or make 

 one by placing a board on four warm 

 tumblers. Present the knuckles of your 

 riirht hand to the end of tho balanced 

 lath, and stretch forth your left arm. 

 There is no attraction. But let n friend 

 or an assistant bring the rubbed glass 

 tube over the left arm ; the kUi immedi- 

 ately follows the right Land. 



Touch the lath, or any (.th'-r uninsulat- 

 ed body ; the ** attractive virtue," as it 

 was called by Gray, disappears. After 

 this, as long r.& the "excited tul is held 



over the arm there in no attraction. But 

 when the tube is removed the attractive 

 power of the hand is restored. Here the 

 first attraction was by positive -electricity 

 driven to the right Land from the left, 

 and the second attraction by negative 

 electricity, liberated by the removal of 

 the glass rod. Experiment proves the 

 logic of theory to be without a flaw. 



Stand on an insulating stool, and place 

 your right hand on the electroscope ; 

 there is no action. Stretch forth the left 

 arm and permit an assistant alternately 

 to bring near, and to withdraw, an excit- 

 ed glass tube. The gold leaves open ?;nd 

 collapse i.i similar alternation. At every 

 approach, positive electricity is driven 

 over the gold leaves ; at every with- 

 drawal, the equilibrium is restored. 



We arc now in a condition to repeat, 

 with case, the experiment of Du Fay- 

 mentioned in 1.,. A board is support- 

 ed by four silk ropes, and on the board 

 is stretched a boy. Bring his fore Lend, 

 or better still his nose, under the end of 

 your straw-index 1 i', fig. 22. Then 

 bring down over his legs your rulbed 

 glass tube ; instantly the end i' is attzact- 

 ed and the end i rises along the graduat- 

 ed scale. Before the end i' comes into 

 contact with the nose or forehead a spark 

 passes between it and the boy. 



