AND MODERN PHYSICS. 153 



observed in electrical and magnetic phenomena. In the case 

 of a perfectly arbitrary system of forces, there will generally 1>3 

 interstices between the tubes ; but in the case of electric and 

 magnetic forces it is possible to arrange the tubes so as to 

 leave no interstices. The tubes will then be mere surfaces, 

 directing the motion of a fluid filling up the whole space. It 

 has been usual to commence the investigation of the laws of 

 these forces by at once assuming that the phenomena are due 

 to attractive or repulsive forces acting between certain joints. 

 We may, however, obtain a different view of the subject, and 

 one more suited to our more difficult inquiries, by adopting for 

 the definition of the forces of which we treat, that they may be 

 represented in magnitude and direction by the uniform motion 

 of an incompressible fluid. 



44 1 propose, then, first to describe a method by which the 

 motion of such a fluid can be clearly conceived ; secondly to 

 trace the consequences of assuming certain conditions of 

 motion, and to jK>int out the application of the method to 

 some of the less complicated phenomena of electricity, 

 magnetism, and galvanism ; and lastly, to show how by an 

 extension of these methods, and the introduction of another 

 idea due to Faraday, the laws of the attractions and inductive 

 actions of magnets and currents may be clearly conceived, 

 without making any assumptions as to the physical nature of 

 electricity, or adding anything to that which has been already 

 proved by experiment 



" By referring everything to the purely geometrical idea of 

 the motion of an imaginary fluid, I hope to attain generality 

 and precision, and to avoid the dangers arising from a pre- 

 mature theory professing to explain the cause of the 

 phenomena. If the results of mere speculation \\hirh I have 

 collected are found to be of any use to e\i>erimental philo- 

 sophers, in arranging and interpreting their results, they will 

 have served their purpose, and a mature theory, in which 

 physical facU will be physically explained, will be formed by 

 those who by interrogating Nature herself can obtain the only 

 true solution of the questions which the mathematical theory 

 suggests," 



