LESSONS IN ELECTRICITY. 



231 



power, wliich it exercises, of condensing 

 upon its surface into a liquid film, the 

 {i < I neons vapor of the surrounding air. 

 This film must be removed. 



1 would also insist on practice, in order 

 to render you expert. You will therefore 



attract bran, scraps of paper, gold leaf, 

 soap bubbles, and other light bodies by 

 rubbed glass, sealing-wax, and gutta- 

 perciia. Faraday was fond of making 

 empty egg shells, hoops of paper, and 

 other light objects roll after his excited 

 tubes. 



It is only when the electric power is 

 very weak, that you require your deli- 

 cately suspended straw. With the sticks 

 of wax, tubes, and rubbers here men- 

 tioned, even heavy bodies, when properly 

 suspended, may be attracted. Place, for 

 instance, a common walking stick in the 

 wire loop attached to the narrow ribbon, 

 fig. .1, ;md let it swing horizontally. The 

 glass, rubbed with its silk, or the sealing- 

 wax, or gutta-percha, nibbed with its 

 flannel, will pull the stick quite round. 



Abandon the wire loop ; place an egg 

 in an (gg-cup, and balance a long lath 

 upon the egg, as shown in fig. 4. The 

 lath, though it may be almost a plank, 



will obediently follow the rubbed glass, 

 gutta-percha, or sealing-wax. 



Nothing can be simpler than this lath 

 and egg arrangement, and hardly any- 

 thing could be more impressive. The 

 more you work with it, the better you 

 will like it. 



Pass an ebonite comb through the 

 hair. In dry weather it produces a 

 crackling noise ; but its action upon the 

 lath may be made plain in any weather. 

 It is rendered electrical by friction against 

 the hair, and with it you can pull the lath 

 quite round. 



If you moisten the hair with oil, the 

 comb will still be excited and exert at- 

 traction ; but if you moisten it with 

 water, the excitement ceases ; a comb 

 passed through wetted hair has no power 

 over the lath. You will understand the 

 meaning of this subsequently. 



After its passage through, dry or oiled 

 hair, balance the comb itself upon the 

 egg : it is attracted by the lath. You 

 thus prove the attraction to be mutual : 

 the comb attracts the lath, and the lath 

 attracts the comb. Suspend your rubbed 

 glass, rubbed gutta-percha, and rubbed 

 sealing-wax in jour wire loep. They are 

 all just as much attracted by the lath as 

 the lath was attracted by them. This is 

 an extension of Boyle's experiment witk 

 the suspended amber (2). 



IIovv it is that any unelectrificd body 

 attracts, and is attracted by the excited 

 glass, sealing-wax, and gutta-percha, we 

 shall learn by and by. 



A very striking illustration of electric 

 attraction may be obtained with the board 

 and india-rubber mentioned in our list of 

 materials (4). Place the board before 

 the fire and make it hot ; heat also a 

 sheet of foolscr.p paper and place it on 

 the board. There is no attraction be- 

 tween them. Pass the india-rubber brisk- 

 ly over the paper. It now clings firmly 

 to the board. Tear it away, arid hold jt 

 at arm's length, for it will move to your 

 body if it can. Bring it near a door or 

 wall, it will cling tenaciously to either. 

 The electrified paper also powerfully at- 

 tracts tho balanced lath from a great dis- 

 tance. 



The friction of the hnnd, of a cam- 

 bric handkerchief, or of wash-leather 

 fails to electrify the paper in any high 

 degree. It requires friction by a 



