PREFACE TO THE FIFTH EDI1ION. xi 



To show that the work of to-day is not substantially 

 different from the thoughts I first published on the 

 subject, at a period when I knew little or nothing of 

 what had been thought before, I venture to give a few 

 extracts from the printed copy of my lecture of 1842: 



Physical Science treats of Matter, and what I shall to-night 

 term its Affections ; namely, Attraction, Motion, Heat, Light, 

 Electricity, Magnetism, Chemical-Affinity. When these re-act 

 upon matter, they constitute Forces. The present tendency of 

 theory seems to lead to the opinion that all these Affections 

 are resolvable into one, namely, Motion : however, should 

 the theories on these subjects be ultimately so effectually 

 generalised as to become laws, they cannot avoid the 

 necessity for retaining different names for these different 

 Affections ; or, as they would then be called, different Modes 

 of Motion 



QErsted proved that Electricity and Magnetism are two 

 forces which act upon each other ; not in straight lines, as all 

 other known forces do, but in a rectangular direction : that is, 

 that bodies invested with electricity, or the conduits of an 

 electric-current, tend to place magnets at right angles to 

 them ; and, conversely, that magnets tend to place bodies 

 conducting electricity at right angles to them 



The discovery of CErsted, by which electricity was made 

 a source of Magnetism, soon led philosophers to seek the con- 

 verse effect ; that is, to educe Electricity from a permanent 

 magnet. Had these experirhentalists succeeded in their ex- 

 pectations of making a stationary magnet a source of electric- 

 currents, they would have realised the ancient dreams of 

 perpetual motion, they would have converted statics into 

 dynamics, they would have produced power without expen- 

 diture ; in other words, they would have become creators. 

 They failed, and Faraday saw their error : he proved that to 



