14U 



ELECTRICITY. 



Lesson IV. 



the electricity is less equally distributed 

 over its surface, and collects at points 

 Iving farthest from the* middle. 

 " 44. 7. Do po ; n'e<l bodies affect the 

 accumulation of elec'ricity? 



P. Yes. If a point is brought near an 

 insulated conductor, the electricity will be 

 more dense at that part, und therefore 

 overcome the resistance of the air, which 

 envelopes it. as if it were a non-conducting 

 layer. Experim nts prove that electricity 

 flows readily from sha r p-pointed bodies. 



45. T. Is the knowledge of the in- 

 fluence of pointed bodies practically ap- 

 plied ? 



P. Yes, in the construction of light- 

 ning conductors. 



46. T. Suppose that we place two 

 insulated electric conductors, similarly 

 charged, near to each other, how will the 

 electr city be distributed on their sur- 

 faces ? 



P. The electric density will diminish 

 between the conductors as they are placed 

 near to eaeh other, arid increase at those 

 points furthest from the point between 

 the two, thus : 



Of* The sphere a b, and the sphere 

 *J c d, when insulated, and placed 

 a I b c * d near to each other, if charged 

 Fig. 16. M j tn the same electricity, will 

 cause a disturbance. The electricity of 

 one sphere will repel that of the other, 

 and therefore at b and c the density of the 

 electricity decreases, while it increases at 

 a and d. The nearer the spheres are 

 brought together, the greater will he the 

 increase of intensity at a and d, and the 

 diminution at b and c. 



47. T. What would be the effect of 

 bringing a non electric conductor near to 

 an electrified insulated conductor? 



P. It would become electric by in- 

 duction, and act like a body charged with 

 the opposite electricity. 



48. T. Suppose that the two spheres 

 (Fig. 1G) are placed in contact, what will 

 be the effect? 



P. The density of the electricity will 

 be null where they' touch. If these spheres 

 had been charged with opposite electric! 

 ties, then the matter would be reversed, 

 and on bringing the spheres together a 

 spark would be produced, because the 

 density of the electricity would be at 

 b and c instead of a and d. 



49 /' The two spheres a b and c d, 

 Fig 16, are charged with opposite elec- 

 tric. ties, the former with + ,and the latter 

 with el crricity. New the electricity 

 of the one sphere is attracted by that of 

 the opposite sphere, nnd being prevented 

 from escaping they comb ne. How must 

 we manage to make the combination 

 perfect? 



P. By separating the spheres with a 

 Franklin pl.i e. 



50. T. Explain what you mean by a 

 Fr.mklin plate, and its mode of action 



P. It is a plate of glass, partially 

 coated on both sides with 

 tin foil (o Fiy. 17), so as 

 to leave the outer part 

 free. If this plate is placed 

 between the two spheres, 

 theone part will be charged 

 with + and the other with 

 electricity, so that the 

 glass alone separates them; 

 and ;is they are unable 

 to penetrate the glass the 

 combination is pretty per- 

 fect> 



51. T. Is it necessary to bring both 

 sides of the Franklin plate into contact 

 with the spheres to charge its sides with 

 opposite electricity ? 



P. No, because by charging the front 

 side with + electricity it will act by- 

 induction upon the combined electricities 

 of the other side ; and as soon as we 

 place that side in connection with the 

 earth, the + electricity will pass into the 

 earth, and the electricity will be in- 

 duced to the back surface As the 

 electricity of the back surface repels the 

 f electricity of the front surface, it 

 enables electricity to pass again from 

 the conductor to the front surface, which 

 again repels it, and thus increases the 

 electricity of the back surface. By acting 

 in this manner, we may charge one surface 

 with +, and the other with electricity. 

 52. T. How can we 

 make this plate discharge 

 its electricity at once? 



P. By means of the 

 discharging - rod {Fiy, 

 18), which, as it touches 

 both surfaces at once, 

 puts them into con- 

 nection with each other, 



Fiy, 18. 



