A LECTURE ON MAGNETISM. 375 



Now, I think, without further preface, you will be able 

 to comprehend for yourselves, and explain to others, one 

 of the most interesting effects in the whole domain of 

 magnetism. Iron filings you know are particles of iron, 

 irregular in shape, being longer in some directions than in 

 others. For the present experiment, moreover, instead of 

 the iron filings, very small scraps of thin iron wire might be 

 employed. I place a sheet of paper over the magnet ; it is 

 all the better if the paper be stretched on a wooden frame, 

 as this enables us to keep it quite level. I scatter the 

 filings, or the scraps of wire, from a sieve upon the paper, 

 and tap the latter gently, so as to liberate the particles for 

 a moment from its friction. The magnet acts on the filings 

 through the paper, and see how it arranges them ! They 

 embrace the magnet in a series of beautiful curves, which 

 are technically called magnetic curves, or lines of magnetic 

 force. Does the meaning of these lines yet flash upon 

 you ? Set your magnetic needle or your suspended bit of 

 wire at any point of one of the curves, and you will find 

 the direction of the needle or of the wire to be exactly that 

 of the particle of iron, or of the magnetic curve at the 

 point. Go round and round the magnet ; the direction of 

 your needle always coincides with the direction of the curve 

 on which it is placed. These, then, are the lines along 

 which a particle of south magnetism, if you could detach it, 

 would move to the north pole, and a bit of north magnetism 

 to the south pole ; they are the lines along which the de- 

 composition of the neutral fluid takes place, and in the case 

 of tfie magnetic needle, one of its poles being urged in one 

 direction, and the other pole in the opposite direction, the 

 needle must necessarily set itself as a tangent to the curve. 

 I will not seek to simplify this subject further. If there 

 be any thing obscure or confused or incomplete in my 

 statement, you ought now, by patient thought, to be able 

 to clear away the obscurity, to reduce the confusion to 



