NATUKAL PHILOSOPHY. 125 



curious action which accompanies the act of magnetization I will now 

 try to make sensible to you. Other men labored, and we are here 

 entering into their labors. The effect I wish to make manifest was 

 discovered by Mr. Joule, and was subsequently examined by MM. 

 De la Hive, Wertheim, Marian, Matteucci, and Wartmann. It is this. 

 At the moment when the current passes through the coil surrounding 

 the electro-magnet, a clink is heard emanating from the body of the 

 iron, and at the moment the current ceases a clink is also heard. In 

 fact, the acts of magnetization and demagnetization so stir the atoms 

 of the magnetized body that they, in their turn, can stir the air and 

 send sonorous impulses to our auditory nerves. 



I have said that the sounds occur at the moment of magnetization, 

 and at the moment when magnetization ceases ; hence if I can devise 

 a means of making and breaking in quick succession the circuit 

 through which the current Hows, I can obtain an equally quick suc- 

 cession of sounds. I do this by means of a contact breaker which 

 belongs to a lluhmkorff's induction coil. Here is a monochord, and 

 a thin bar of iron stretches from one of its bridges to the other. 

 This bar is placed in a glass tube, which is surrounded by copper 

 wire. I place the contact breaker in a distant room, so that you can- 

 not hear its noise. The current is now active, and every individual 

 in this large assembly hears something between a dry crackle and a 

 musical sound issuing from the bar in consequence of its successive 

 magnetization and demagnetization. 



Magnetism of the Electric Current. Hitherto we have occupied 

 ourselves with the iron which has been acted upon by the current. 

 Let us now devote a moment's time to the examination of the current 

 itself. Here is a naked copper wire which is quite inert, possessing 

 no power to attract these iron filings. I send a voltaic current 

 through it : it immediately grapples with the filings, and holds them 

 round it in a thick envelop. I interrupt the current, and the filings 

 fall. Here is a compact coil of Copper wire, which is overspun with 

 cotton to prevent contact between the convolutions. At present the 

 coil is inert ; but now I send a current through it : a power of attrac- 

 tion is instantly developed, and you see that it is competent to empty 

 this plate of iron nails. 



Thus we have magnetic action exhibited by a body which does not 

 contain a particle of the so-called magnetic metals. The copper wire 

 is made magnetic by the electric current. Indeed, by means of a cop- 

 per wire, through which a current Hows, we may obtain all the effects 

 of magnetism. I have here a long coil, so suspended as to be capable 

 of free motion in a horizontal direction ; it can move all round in a 

 circle like an ordinary magnetic needle. At its ends I have placed two 

 spirals of platinum wire, which the current will raise to brilliant 

 incandescence. They are glowing now, and the suspended coil be- 

 haves, in all respects, like a magnetic needle. Its two ends show 

 opposite polarities ; it can be attracted and repelled by a magnet, or 

 by a current ilowing through another coil ; and it is so sensitive that 

 the action of the earth itself is capable of setting it north and south. 



Ampere's Theory. There is an irresistible tendency to unify in the 

 human mind ; and, in accordance with our mental constitution, we 

 desire to reduce phenomena which are so much alike to a common 

 11* 



