386 Mr Murphy on the Inverse Method of 



SECTION III. 



APPLICATION OF THE PRECEDING PRINCIPLES, TO THE PHENOMENA 

 OF DEVELOPED ELECTRICITY. {Plate 24). 



25. When a body is electrised, either by communication, by 

 influence, or in any other manner, from known or unknown 

 causes, the external action is subject to observation. The law 

 of the action of an electrical particle, at different distances, is 

 at the same time, known to vary as the inverse square of the 

 distance. To find the nature of the electric distribution necessary 

 for the production of any given phenomenon, is evidently a 

 mathematical problem, the solution of which may easily be sub- 

 jected to the test of experiment. As it is also peculiarly adapted 

 to illustrate the analytical principles which precede, we have taken 

 it as the subject of this Section. 



26. (Fig. 3.) For the external action, it will be generally 

 convenient to substitute the electrical tension at the different 

 points (Q) of an infinitely thin, conducting rod (Bx), communi- 

 cating with the electrised body APB. This tension is the sum 

 of the quotients when we divide the mass of each electrical 

 particle, by the distance of that particle from Q. 



27. Suppose the figure APB spherical, and that the electric 

 tension in the rod Ax passing through the centre, at any point 

 Q in the external part is found to be inversely as the distance 



