6iz THE POPULAR SCIENCE MONTHLY. 



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 attraction ; but, if you moisten it with water, the excitement 

 ceases ; a comb passed through wetted hair has no power over the 

 lath. 



After its passage through dry or oiled hair, balance the comb it- 

 self 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 your wire loop. 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 with the suspended amber. 



How it is that the unelectrified lath attracts, and is attracted by 

 the excited glass, sealing-wax, and gutta-percha, we shall learn by- 

 and-by, 



A very striking illustx-ation of electric attraction may be obtained 

 with the board and India-rubber mentioned in our list of materials. 

 Place the board before the fire and make it hot ^ heat also a sheet of 

 foolscap paper and place it on the board. There is no attraction be- 

 tween them. Pass the India-rubber briskly over the paj^er. It now 

 clings firmly to the board. Tear it away, and hold it 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 attracts the balanced lath from a great distance. 



The friction of the hand, of a cambric handkerchief, or of wash- 

 leather, fails to electrify the paper in any high degree. It requires 

 friction by a special substance to make the excitement strong. This 

 we learn by experience. It is also experience that has taught us that 

 resinous bodies are best excited by flannel, and vitreous bodies by silk. 



Take nothing for granted in this inquiry, and neglect no effort to 

 render your knowledge complete and sure. Try various rubbers, and 

 satisfy yourself that difterences like that first observed by Newton 

 exist between them. 



Lay bare, also, the true influence of heat in our last experiment. 

 Spread a cold sheet of foolscap on a cold board on a table, for 

 example. If the- air be not very dry, rubbing, even with the India- 

 rubber, will not make them cling together. But is it because they 

 were hot that they attracted each other in the first instance ? No, 

 for you may heat your board by plunging it into boiling water, and 

 your paper by holding it in a cloud of steam. Thus heated they 

 cannot be made to cling together. The heat really acts by expel- 

 ling the moisture. Cold weather, if it be only dry, is highly favor- 

 able to electric excitation. During the late frost the wiiisking of 

 the hand over silk or flannel, or over a cat's back, would have ren- 

 dered it electrical. 



