

v 



Lesson VII. 



There is a law which is called the electrolytic law, that no electric current, or com- 

 p;ir.!tivi-ly only a very weak one, can pass through a lluid without its passage bein;: 

 j by chemical decomposition. This occurs in every cell of every galvanic- 

 apparatus as long as the circuit is complete, and the quantity of the electric current i> 

 proportionate to the amount of decomposition in each cell. 



We have now to consider other actions of the galvanic current its magnetic 

 actions. For a considerable period it had been known that powerful electric charges, 

 under certain circumstances, affected the magnetic needle. Experiments were made, 

 but in the year 1820, Oersted discovered a means of causing electricity to act certainly 

 and constantly upon a magnet. 



QUESTIONS. 



S3. T. How can we magnetize soft iron 

 so as to form magnets ? 



P. By passing a current of electricity 

 at right angles to it, in which case the 

 iron will acquire magnetic polarity, either 

 temporary or permanently, as the case may 

 be, the direction of the current determin- 

 ing the position of the poles. [Experiment 

 I have a bar of soft iron in my 

 hand, and you observe 

 that it is bent into the 

 form of a horse-shoe ; 

 here is some copper wire 

 which is covered with 

 silk for the purpose of 

 insulation, and you ob- 

 serve that I have now 

 wound it firmly over the 

 bar of iron, so that the 

 windings are all close 

 togc-ther; we will sus- 

 pend the horse- shoe bar 

 to a hook in the beam 

 by means of the ring at 

 the top of it. [Does so ] 

 Tig. 25. Now let us try if it \vi:i 



support the keeper, or even an iron nail. 

 [Tries them, and they fall to the ground.] 

 Let us place the ends of the wire into 

 communication with a small voltaic bat- 

 tery, and try the keeper again. [Does so, 

 and the keeper adheres firmly, so as to be 

 able to bear a very heavy weight as in 

 /'/<;. 2.j.] If we disconnect the wires, the 

 weight and keeper will fall to the ground. 

 [Does so, and they instantly fall.] 



84. T. Which is the north, and which 

 the south pole of this magnet ? 



P. Where the + current enters, a 

 north pole is formed, and a south pole 

 where the current enters. 



sf>. T. Then it would appear that the 



wire of an electric current is a magnet. 

 Is this the case ? 



P. Certainly; arid it shows attractions 

 and repulsions for other electric wires. 

 For example, if the wires of two circuits 

 are placed side by side, and are free, they 

 will be mutually repelled if the direction 

 of the current is the same iu both, and 

 attracted if the currents are contrary. 



86. T. Can motion be produced by 

 the galvanic current? 



P. Yes ; a continuous motion may be 

 produced by the magnetizing action of the 

 galvanic current ; but the apparatus is too 

 extensive for me to demonstrate it to you. 

 Attempts have been made by Jacobi, of 

 St. Petirsburgh, and Wagner, of Frank- 

 fort, to apply the galvanic current prac- 

 tically as a moving power ; but the expense 

 is a seriojs objection to its use. 



87. T. Has any practical application 

 been made of the magnetization of soft 

 iron by galvanic currents ? 



P. Yes, iu the construction of the 

 electric telegraph, the arrangements of 

 which admits of a perfect correspondence 

 being carried on, resulting from attraction 

 and repulsion. 



88. T. What do you mean by thermo- 

 electricity ? 



P. It is simply electricity, developed 

 by heat. 



89. T. How is this produced ? 



p. We know that an electric current 

 develops heat on passing through an infe- 

 rior conducting substance, or if its passage 

 is interrupted. This is by no means any- 

 thing new ; but within the last twenty 

 years, Professor Seebeck, of Berlin, has 

 discovered that heat may be made to pro- 

 duce a current of electricity. This is 

 managed as follows : two metals are sol- 



