6 PREFACE. 



The discovery of (Ersted, by which electricity was made a source of 

 Magnetism, soon led philosophers to seek the converse effect ; that is, to 

 educe Electricity from a permanent magnet : had these experimentalists 

 succeeded in their expectations 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 expenditure ; in other-words, they would have be- 

 come creators. They failed, and Faraday saw their error ; he proved that 

 to obtain Electricity from Magnetism it was necessary to superadd to this 

 latter, motion ; that magnets while in motion induced electricity in con- 

 tiguous conductors ; and that the direction of such electric-currents was 

 tangential to the polar direction of the magnet ; that as Dynamic-electricity 

 may be made the source of Magnetism and Motion, so Magnetism conjoined 

 with Motion may be made the source of Electricity. Here originates the 

 Science of Magneto-electricity, the true converse of Electro-magnetism; 

 and thus between Electricity and Magnetism is shown to exist a reciprocity 

 of force such that, considering either as the primary agent, the other be- 

 comes the re-agent ; viewing one in the relation of cause, the other is the 

 effect 



The Science of Thermo-Electricity connected heat with electricity, and 

 proved these, like all other natural forces, to be capable of mutual reac- 

 tion 



Voltaic action is Chemical action taking place at a distance or trans- 

 ferred through a chain of media ; and the Daltonian equivalent numbers 

 are the exponents of the amount of voltaic action for corresponding chemi- 

 cal substances. . . . 



By regarding the quantity of electrical, as directly proportional to the 

 efficient chemical action, and by experimentally tracing this principle, I 

 have been fortunate enough to increase the power of the Voltaic-pile 

 more than sixteen times, as compared with any combination previously 

 known 



I am strongly disposed to consider that the facts of Catalysis depend 

 upon voltaic action, to generate which three heterogeneous substances are 

 always necessary. Induced by this belief I made some experiments on the 

 subject, and succeeded in forming a voltaic combination by gaseous-oxygen, 

 gaseous-hydrogen, and platinum ; by which a galvanometer was deflected 

 and water decomposed 



It appears to me that heat and light may be considered as affections ; 

 or, according to the Undulatory-theory, vibrations of matter itself, and not 

 of a distinct etherial fluid permeating it : these vibrations would be prop- 

 agated, just as sound is propagated by vibrations of wood or as waves by 

 water. To my mind, all the consequences of the Undulatory-theory flow 

 as easily from this, as from the hypothesis of a specific ether ; to suppose 

 which, namely, to suppose a fluid sui generis, and of extreme tenuity pene- 

 trating solid bodies, we must assume, first, the existence of the fluid itself; 

 secondly, that bodies are without exception porous; thirdly, that these 

 pores- communicate; fourthly, that matter is limited in expansibility. 

 None of these difficulties apply to the modification of this theory which I 

 venture to propose ; and no other difficulty applies to it which does not 

 equally apply to the received hypothesis. With regard to the planetary 

 spaces, the diminishing periods of comets is a strong argument for the ex- 

 istence of an universally-diffused matter : this has the function of resist- 



