Principles of the Science of Motion. 51 - 
effect of differential molecular action, that a better conductor 
will, in moving in the direction of least resistance, pass to a 
‘stronger place of action. 
The above conclusions are Faraday’s*; but the theorem and 
corollary as generalizations rest also on the facts adduced by 
Ampére and his successors in support of his helix-theory of the 
magnet. 
A third most important class of facts by which the view here 
given of the mechanical conditions of the electric motions of 
bodies may be supported, is the disposition of iron filings about 
one or more electrified wires or magnets in various positions, 
and the information given by a moving wire as to magnetic 
forces. 
26. The fundamental importance of the conceptions of a force 
as, in general, a difference of pressures, and of polar attraction 
and repulsion as the effect of a differential molecular action, has 
induced me to give such disproportioned length to their illustra- 
tion, that it will be impossible within the brief limits of this 
paper todo more than note the other chief points of this general 
theory. 
What, therefore, has to be said on (B) (8) the effects of 
electricity as manifested in motions of the medium, must be 
referred to the paragraph on the correlation of forces. 
27. There will not, it is hoped, be thonght to be presump- 
tion in offering new views in theories which have been elaborated 
with such admirable genius as those of light and heat ; for the 
most strenuous supporters of the present form of the undulatory 
theory candidly admit that “there undoubtedly are several 
classes of phenomena which the wave theory has not merely 
failed to explain, but which are apparently at direct variance with 
its principles +.” 
It will be evident that the chief new view necessitated by this 
general theory (and which alone can be here noticed) resolves 
itself into a theory of the connexion of the elastic medium with 
the vibrating molecules in it. Now, though according to the 
present theory “it is certain that light is produced by undulations 
propagated with transversal vibrations through a highly elastic 
ether, yet the constitution of this ether, and the laws of its 
connexion (if it has any connexion) with the particles of bodies, 
are utterly unknown{.” But the theory here proposed implies 
such “laws of connexion.” For its practical result is, that the 
“ether” is conceived as the mutually determined lines of 
* But compare Tyndall’s Memoirs ‘‘ On the Reverse Polarity of Bis- 
muth” (Phil. Trans. 1855 and 1856). 
+ Baden Powell, ‘ Undulatory Theory,’ Introduction, p. xxiv. 
~ MacCullagh, ‘“ Laws of Crystalline Reflexion,” &c., Mem, R.I. A., 
Xvi. 38, 
K2 
