382 FRAGMENTS OF SCIENCE 



ranges 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 that point. Go 

 round and round the magnet; the direction of your nee- 

 dle always coincides with the direction of the curve OD 

 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 mag- 

 netism to the south pole. They are the lines along which 

 the decomposition of the neutral fluid takes place. In the 

 case of the magnetic needle, one of its poles being urged 

 in one direction, and the other pole in the opposite direc- 

 tion, the needle must necessarily set itself as a tangent 

 to the curve. 



I will not seek to simplify this subject further. If 

 there be anything 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 order, and to supply what is needed to ren- 

 der the explanation complete. Do not quit the subject 

 until you thoroughly understand it; and if you are then 

 able to look with your mind's eye at the play of forces 

 around a magnet, and see distinctly the operation of those 

 forces in the production of the magnetic curves, the time 

 which we have spent together will not have been spent 

 in vain. 



In this thorough manner we must master our materials, 



