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 " * 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- 



