LESSOKS 



Attract your straw needle by your rub- 

 bed glass tube. Let the straw strike the 

 tul>e, so that the one shall rub against 

 the other. The straw accepts the elec- 

 tricity of the tube, and repulsion immedi- 

 ately follows attraction, as shown in fig. 

 9. 



Mr. Cuttrcll has devised the simple 

 electroscope represented in fig. 10 to 

 snow repulsion. A is a stem of sealing- 

 wax with a small circle of tin, T, at the 

 top. w is a bent wire proceeding from 

 T, with a small disk attached to it by 

 wax. i i' is a little straw index, support- 

 ed by the needle N, as shown in fig. 10. 

 The stem A', also of sealing-wax, is not 

 quite vertical, the object being to cause 

 the bit of paper, i', to rest close to w 

 when the apparatus is not electrified. 

 When electricity is imparted to T, it 

 f.ows through the wires w and w, over 

 both disk and index : immediate repul- 

 sion of the straw is the consequence. 



No better experiment can be made to 

 illustrate the self-repulsive character of 

 electricity than the following one. Heat 

 your square board ( 5), and warm, as 

 before, your sheet of foolscap. Spread 

 the paper upon the board, and excite it 

 by the friction, of india-rubber. Cut 

 from the sheet two long strips with your 



penknife. Hold the stiips together at 

 one end. Separate them from the board, 

 and lift them into the air : they forcibly 

 diive each other apart, producing a wide 

 divergence. 



Cut r.-.rveral stiips. so as to form a kind 

 of tassel. Hold them together at one 

 end. Separate them from the board, and 

 lift them into the air : they are driven 

 asunder by the self-repellent electricity, 

 presentini*" an appearance which may ie- 

 mind you of the hair of Medusa. The 

 effect is represented in fig. 11.* 



Another very beautiful experiment fits 

 in here. Let fine silver sand, s, fig. 12, 

 issue in a stream from a glass funnel, 

 through an aperture one eighth of an inch 

 in diameter. Connect the sand in the 

 funnel by a fine wire w, fig. 13, with your 

 warm g-lass tube. Unelectrified, the 



* In one of my earliest lectures at the 

 Royal Institution, having rubbed a sheet of 

 foulscap, I was about lo lii't it bodily from 

 the hot board, and to place it against the 

 wall, when the thought of cutting it into 

 strips, and allowing them to net upon each 

 other, orciirnd to me. The itsult, of 

 course, was that above described. Simple 

 and obvious as it was. it gave Faraday, who 

 was present at the time, the most lively 

 pleasure. The simplest experiment, if only 

 suited to its object, delighted him. 



