16 INTRODUCTORY OBSERVATIONS. 



surface, here found, agrees with the one long since deduced from 

 other methods. 



Thus far perfect conductors only have been considered. In 

 order to give an example of the application of theory to bodies 

 which are not so, we have, in the thirteenth article, supposed the 

 matter of which they are formed to be endowed with a constant 

 coercive force equal to /5, and analogous to friction in its opera- 

 tion, so that when the resultant of the electric forces acting upon 

 any one of their elements is less than /3, the electrical state 

 of this element shall remain unchanged; but, so soon as it 

 begins to exceed /3, a change shall ensue. Then imagining a 

 solid of revolution to turn continually about its axis, and to be 

 subject to a constant electrical force f acting in parallel "right 

 lines, we determine the permanent electrical state at which the 

 body will ultimately arrive. The result of the analysis is, that 

 in consequence of the coercive force /3, the solid will receive a 

 new polarity, equal to that which would be induced in it if it 

 were a perfect conductor and acted upon by the constant force 

 /3, directed in lines parallel to one in the body's equator, making 

 the angle 90 + 7, with a plane passing through its axis and 

 parallel to the direction of/ : / being supposed resolved into two 

 forces, one in the direction of the body's axis, the other b 

 directed along the intersection of its equator with the plane just 

 mentioned, and 7 being determined by the equation 



In the latter part of the present article the same problem is 

 considered under a more general point of view, and treated by a 

 different analysis : the body's progress from the initial, towards 

 that permanent state it was the object of the former part to de- 

 termine is exhibited, and the great rapidity of this progress made 

 evident by an example. 



The phenomena which present themselves during the rota- 

 tion of iron bodies, subject to the influence of the earth's mag- 

 netism, having lately engaged the attention of experimental 

 philosophers, we have been induced to dwell a little on the 

 solution of the preceding problem, since it may serve in some 

 measure to illustrate what takes place in these cases. Indeed, 



