and Transmission of Power. z 5 



All magnets have innumerable " lines of force," as they are 

 technically called, in their vicinity; and unmistakable evidence 

 of their existence is obtained when iron filings are brought 

 within their influence. The filings cluster more densely near 

 the ends of the magnet than at the centre, and they appear to 

 arrange themselves in arcs of curves from one extremity to the 

 other. In Fig. No. 3 on the screen, a novel arrangement of 

 apparatus is shown, consisting of a magnet held between two 

 sheets of glass. There is a third sheet of glass fastened at a 

 little distance from the others, thus allowing a space in which 

 iron filings can be scattered ; thus the process in which they 

 arrange themselves in the direction of the lines of force can be 

 observed. 



Soft iron or steel may not only be magnetised by proximity 

 to another magnet, but it may also be acted upon to a far greater 

 extent by wrapping insulated wire upon it, and sending a current 

 along the wire. If the current is again passed along the wire ' 

 in the opposite direction, the end which was formerly a North 

 Pole is now a South. Faraday made the discovery that if a coil 

 of wire with its ends connected together was moved in a certain 

 manner near to a magnet, a powerful current was generated in 

 the wire. Of course if the ends of the wire were not joined, no 

 current was developed, as in all cases where a current passes 

 along a wire, the circuit must be completed, either by direct 

 connection of the ends, or by the interposition of some con- 

 ducting medium, such as the earth or liquids, more especially 

 if the latter are acidulated. Even in the case of "arc" electric 

 lighting, although it may at first sight appear as if the circuit 

 was broken between the carbons, as indicated by Fig. 4 on 

 the screen, yet the continuity of the conducting medium is 

 maintained by the intensely heated air at the point of sepa- 

 ration, and by the particles of carbon which jump across the 

 space. As the polarity of the magnet can be changed by 

 reversing the direction in which the exciting current flows, so 

 can the direction of the current in the coil be altered by changing 

 the position of the poles of the magnet. In Fig. 5, the coil is 

 supposed to move from left to right, or from the North pole 



