132 



r.l.KcTL.UTV. 



\cite the properties you have men- 

 tioned ? 



^'.[Experiment 1.] Here is a glass 

 rod, and you see that when I touch the 

 pieces of paper, elder-pith balls, feathers, 

 and sawdust that are upon the table, that 

 no change takes place. I will try this 

 rod of brimstone. (Does so.) You see 

 that there is no change ; and if I were to 

 try a piece of amber or sealing-wax it 

 would be just the same. [Experiment 2.] 

 I will now rub the glass rod with my silk 

 handkerchief, which is quite dry. (Does 

 so.) You observe that the pieces of paper, 

 pith, balls, feathers, &c., are attracted 

 (see Fiy. 1) towards the rod, and if we 

 rubbed the amber, sulphur, or sealing- 

 M-ax, the same effect would be produced. 

 The cause of the phenomenon you have 

 witnessed is called Electricity. 



[The pupil should try Experiment 2, in the 

 dark, and he will observe faint luminous 

 flashes, aivl sparks, with a cr.ickling noise, 

 and peculiar odour. Let him repeat the 

 experiment, and use oiled silk sprinkled 

 over with Mosaic gold, or aurum musivum, 

 or mosaicum.* 



5. 7*. How do you know whether a 

 body will become electrical by friction ? 



P. By using the electrical pendulum. 

 (See Fig. 2.) It consists of a piece of 

 wire, bent as 

 you see here, 

 and inserted 

 into a glass 

 stand at one 

 end, while 

 the other end 

 supports a 

 pith -ball, 

 which is sus- 

 pended by a 

 n' n e linen 

 thread. If we place a body near the ball 

 and it is not attracted, it is either non-elec- 

 tric or too slightly electric to produce any 

 effect. It we rub resin, amber, sulphur, and 



* For the method of preparing aun.m tnosai- 

 cvm, see Family Frit-iid, vol. ii. p. 56. (Old 

 Series.) 



Lessen I. 



glass, and apply them to the pith- hah, we 

 shall observe that a sensible effect is pro- 

 duced upon it, for it is either attracted 

 towards the substance presented, or it is 

 repelled. Some bodies, such as wood, 

 charcoal, and precious stones, scarcely 

 produce any attraction and if we rub a 

 metal we do not observe the least attrac- 

 tion. 



6. T. From what you have stated it 

 would appear that some bodies beemne 

 electrical by friction, and others do not 

 acquire such a property by that means. 

 Is it so? 



P. Yes : bodies are divided into con- 

 ductors and non-conductors. The former 

 called aneleclric bodies, and the latter idio- 

 eleclric bodies. 



7. 7". Enumerate the non-conductors. 

 P. Shell-lac, sulphur, amber, jet; all 



resinous bodies, pitch and wax ; gums, 

 including india-rubber and camphor; all 

 vitreous and vitrified bodies ; precioiu' 

 stones, gutta percha, bituminous sub- 

 stances, silk, dried furs, and skins, hair. 

 wool, feathers, paper, porcelain, turpen- 

 tine, various oils and fatty fluids, choca. 

 all dry gases, the atmosphere, steam of 

 high elasticity, ice at Fahr. 



8. T. Enumerate the conductors. 



P. All metals, well-burned and dry- 

 charcoal, plumbago, concentrated and di- 

 luted acids, saline fluids, water, moist 

 vegetable matter, living animal matter, 

 flame, smoke, steam. 



9. T. Demonstrate to me that some of 

 the substances you have enumerated 

 possess the properties ascribed to them. 



P. If we use an electrifying machine 

 and develop electricity, we render the 

 conductor of the machine, which is a 

 metallic body, electric. If we bring a 

 metal cylinder, supported on a glass pedes- 

 tal, in contact with the conductor, the 

 metal will be electrified through its whole 

 extent ; if I lay hold of the cylinder, all 

 its electricity will instantly disappear, 

 because the human body is a good con- 

 ductor. 



10. T. Your observations lead me to 

 believe, that all idio-electric bodies or non- 

 conductors are insulators. Am I correct? 



P. Yes ; and all anelectric bodies trans- 

 mit or conduct electricity. A conductor of 

 electricity can, therefore, only be electric 

 while it is insulated or surrounded by 



