ON FAEADAYS LINES OF FORCE. 159 



intensity of the force as well as its direction by the motion of the fluid in 

 these tubes. This method of representing the intensity of a force by the velocity 

 of an imaginary fluid in a tube is applicable to any conceivable system of forces, 

 but it is capable of great simplification in the case in which the forces are such 

 as can be explained by the hypothesis of attractions varying inversely as the 

 square of the distance, such as those observed in electrical and magnetic pheno- 

 mena. In the case of a perfectly arbitrary system of forces, there will generally 

 be 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 points. 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. 



I 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 point out the application of the method to 

 some of the less complicated phenomena of electricity, magnetism, and galvanism ; 

 and lastly to shew 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 assump- 

 tions 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 premature theory professing to explain the cause of the 

 phenomena. If the results of mere speculation which I have collected are found 

 to be of any use to experimental philosophers, in arranging and interpreting 

 their results, they will have served their purpose, and a mature theory, in which 

 physical facts 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. 



