AND MODERN PHYSICS. 151 



action between contiguous parts of a meJium, while the force 

 of attraction is a relation between distant bodies, and yet, if 

 wo knew nothing more than is expressed in the mathematical 

 formulae, there would bo nothing to distinguish between tho 

 one set of phenomena and the other. 



" It is true that, if we introduce other considerations and 

 observe additional facts, the two subjects will assume very 

 different aspects, but the mathematical resemblance of some of 

 their laws will remain, and may still be made Useful in exciting 

 appropriate mathematical idea". 



"It is by the use of analogies of this kind that I have at- 

 tempted to bring before the mind, in a convenient and manage- 

 able form, those mathematical ideas which are necessary to the 

 btudy of the phenomena of electricity. The methods are gener- 

 ally those suggested by the processes of reasoning which are 

 found in the researches of Faraday, and which, though they 

 have been interpreted mathematically by Professor Thomson 

 and others, are very generally supposed to IKJ of an indefinite 

 ami unmathcmatical character, when compared with those 

 employed by tho professed mathematicians. By the method 

 which I adopt, I hope to render it evident that I am not 

 attempting to establish any physical theory of a science iti 

 which I have hardly made a single experiment, and that the 

 limit of my design is to show how, by a Htrict application of 

 the ideas and methods of Faraday, the connection of the very 

 dim-rent orders of phenomena which he has discovered may le 

 clearly placed before the mathematical mind. I shall therefore 

 avoid as much as I can the introduction of any thing which does 

 not serve as a direct illustration of Faraday's methods, or of 

 the mathematical deductions which may be made from them. 

 In treating the simpler parts of the subject I shall use Faraday's 

 mathematical method* a* well as his ideas. When the com- 

 pluxity of the subject requires it, I shall use analytical nutation, 

 btill confining myself to the development of ideas originated Uy 

 the same philosopher. 



" I have in the first place to explain and illustrate the idea 

 of 'lincsof force.' 



*' When a body is electrified in any manner, a small body 



