KINETIC OR MECHANICAL VIEW OF NATURE. 81 



filled with a moving fluid, and the velocity of the flow 

 inversely proportional to the sectional area of the tubes 

 represented the intensity of the force at any point- in 

 space. He also showed how very much simpler the con- 

 ception becomes, if the law of the acting forces is the 

 experimentally established law of the inverse square of 

 the distance. 



This thought of " referring to the purely geometrical 

 idea of the motion of an imaginary fluid " l was the 

 beginning of the now universally adopted view of a 

 very large class of phenomena, and it was at the same 

 time a great step in the development of the kinetic 

 or mechanical view of natural processes. These lines or 

 tubes of force, 2 with which all space surrounding magnets 

 or electrified bodies was supposed to be filled, enabled 

 Maxwell further to give a definite representation of that 



peculiar state of matter of which Faraday had very 



J J 



early formed an indefinite conception, and which he 

 called the " electrotonic state." Thomson had already 

 in 1847 3 shown how the ideas of Faraday, who as early 



1 How little Maxwell originally 

 intended to give a physical theory 

 is seen from the concluding sen- 

 tences of the introduction to his 

 first paper (loc. cit., vol. i. p. 159) : 

 " By referring everything to the 

 purely geometrical idea of the 

 motion of an imaginary fluid, I 

 hope to attain generality and pre- 

 cision, 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 



VOL. II. 



purpose, and a mature theory, in 

 which physical facts will be physi- 

 cally 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." 



2 Faraday had already in 1852 

 spoken of shells and tubes of force, 

 and invented the term sphondyloid 

 to denote the portion of space en- 

 closed between such shells of force 

 ('Exp. Res.,' vol. iii., No. 3271). 



3 In 1847 ('Cambr. and Dubl. 

 Math. Journal,' reprinted in ' Math, 

 and Phys. Papers,' vol. i. p. 76) 

 Thomson wrote that Faraday's 

 theory of electrostatic induction 



Electro- 



