452 ON PHYSICAL LINES OF FORCE. 



at all until a magnet is placed in that part of the field. We are dissatisfied 

 with the explanation founded on the hypothesis of attractive and repellent 

 forces directed towards the magnetic poles, even though we may have satisfied 

 ourselves that the phenomenon is in strict accordance with that hypothesis, and 

 we cannot help thinking that in every place where we find these lines of force, 

 some physical state or action must exist in sufficient energy to produce the 

 actual phenomena. 



My object in this paper is to clear the way for speculation in this direction, 

 by investigating the mechanical results of certain states of tension and motion 

 in a medium, and comparing these with the observed phenomena of magnetism 

 and electricity. By pointing out the mechanical consequences of such hypotheses, 

 I hope to be of some use to those who consider the phenomena as due to the 

 action of a medium, but are in doubt as to the relation of this hypothesis to 

 the experimental laws already established, which have generally been expressed 

 in the language of other hypotheses. 



I have in a former paper* endeavoured to lay before the mind of the 

 geometer a clear conception of the relation of the lines of force to the space 

 in which they are traced. By making use of the conception of currents in a 

 fluid, I shewed how to draw lines of force, which should indicate by their 

 number the amount of force, so that each line may be called a unit-line of 

 force (see Faraday's Researches, 3122) ; and I have investigated the path of 

 the lines where they pass from one medium to another. 



In the same paper I have found the geometrical significance of the " Elec- 

 trotonic State," and have shewn how to deduce the mathematical relations 

 between the electrotonic state, magnetism, electric currents, and the electromotive 

 force, using mechanical illustrations to assist the imagination, but not to account 

 for the phenomena. 



I propose now to examine magnetic phenomena from a mechanical point of 

 view, and to determine what tensions in, or motions of, a medium are capable 

 of producing the mechanical phenomena observed. If, by the same hypothesis, 

 we can connect the phenomena of magnetic attraction with electromagnetic phe- 

 nomena and with those of induced currents, we shall have found a theory 

 which, if not true, can only be proved to be erroneous by experiments which 

 will greatly enlarge our knowledge of this part of physics. 



* See a paper " On Faraday's Lanes of Force," Cambridge Philosophical Transactions, Vol. \. Part i. 

 Page 155 of this volume. 



