MAGNETIC FORCE. 



255 



while supposed to repel each other, they attracted particles in other bodies. 

 Thus they attracted iron. Coulomb asserted that there were two fluids 

 a north and south fluid. Ampere's theory was that magnetic bodies are 

 made up of molecules, round which currents are always circulating in all 

 directions when non-magnetized, but when magnetized the currents all flow 

 in the same direction. The space through which a magnet diffuses its in- 

 fluence was called by Faraday the Magnetic Field. The lines of magnetic 

 force will be understood from the accompanying illustration (fig. 263). If 



Fig. 263. Lines of magnetic force. 



we cover a magnet with a paper and scatter iron filings over it, we shall see 

 the manner in which the filings arrange themselves. They radiate in curves 

 from the poles of the magnet, and are dependent upon its form. If it 

 be a straight bar magnet, evenly magnetized, they will turn inward in oval 

 curves. 



The manner of magnetization has already been mentioned, but here we 

 will give further illustrations of the method of magnetization. Four magnets 

 are used, two being placed with their opposite poles apart, and upon them 



Fig. 264. Magnetization. 



is placed the bar of which a magnet is to be made. Two other magnets 

 separated by a piece of wood are then brought near, and subsequently 

 drawn from the centre to the ends of the bar. This is the separated touch 

 system ; the double touch of Mitchell is completed by moving the upper 

 two magnets from end to end backwards and forwards, and finally lifting 

 them away from the centre. 



A magnet, then, is a bar of steel endowed with certain properties, such as 

 attracting iron, etc. ; and electro-magnetism is the term applied to the pro- 

 duction of magnetism by means of electricity, the medium being the 



