MAGNETISM. 147 



An experiment which I published in 1845 tends, I think, 

 to illustrate this, and in some degree to show the character 

 of the motion impressed upon the molecules of a magnetic 

 metal at the period of magnetisation. A tube filled with the 

 liquid in which magnetic oxide of iron had been prepared, 

 and terminated at each end by plates of glass, is surrounded 

 by a coil of coated wire. To a spectator looking through this 

 tube a flash of light is perceptible whenever the coil is elec- 

 trised, and less light is transmitted when the electrical current 

 ceases, showing a symmetrical arrangement of the minute 

 particles of magnetic oxide while under the magnetic in- 

 fluence. 



In this experiment it should be borne in mind, that the 

 particles of oxide of iron are not shaped by the hand of man, 

 as would be the case with iron filings, or similar minute por- 

 tions of magnetic matter, but being chemically precipitated, 

 are of the form given to them by nature. 



While magnetism is in the state of change above described, 

 it will produce the other forces ; but it may be said, while 

 magnetism is thus progressive, some other force is acting on 

 it, and therefore it does not initiate : this is true, but the 

 same may be said of all the other forces ; they have no com- 

 mencement that we can trace. We must ever refer them 

 back to some antecedent force equal in amount to that pro- 

 duced, and therefore the word initiation cannot in strictness 

 apply, but must only be taken as signifying the force selected 

 as the first : this is another reason why the idea of abstract 

 causation is inapplicable to physical production. To this 

 point I shall again advert. 



Electricity may thus be produced directly by magnetism, 

 either when the magnet as a mass is in motion, or when its 

 magnetism is commencing, increasing, decreasing, or ceasing ; 

 and heat may similarly be directly produced by magnetism. 

 I have, since the first edition of this Essay was published, 

 communicated to the Royal Society a paper by which I think 



