668 Mr. N. P. McCleland on the 



resist any disturbance o£ an electron from its orbit ; in other 

 words, a system containing two eleetrons or more in separate 

 orbits will be more stable than a system containing only one, 

 and the stability of ethylene is to be explained as due to this 

 effect. 



It is convenient to examine what this effect is in the case 

 of currents. 



Let there be two circuits in which constant currents u, v 

 flow. Let them be slightly displaced a distance 80 in the 

 coordinate 6 during a time St. 



Let w + ^, v + rj be the currents at time t. 



We shall then obtain the following equations: — 



SM . 



SM . 

 Mo£+Ni, + S*+-^0(t£ + g)=.O, 



M being the initial value of M. 



And if initially f, 97, f, 97 are all zero, I e. if the currents 

 are not changed impulsively, we get at the end of time St 



SM N^-Mu -a 

 *- Id LN-M 2 ' 



SM Lu-Mv m 



v= --8em=w 



Therefore, at the end of the motion, and before the currents 

 die away on account of resistance, the force between the 



circuits, instead of being uv -^-, is 



SM _ Lu 8 -2MMr + Nr* f 8M 1 

 UV W " LN-M 2 \c0 J 



he. 



Thus in addition to the ordinary force between the circuits 

 a force is called in to check the motion. We will call this 

 new force — SS0, where S is essentially positive so long as 



LN>M 2 *. 



* The following example may make the above clearer. Imagine a 

 shallow cup filled with liquid and a particle resting at the bottom. The 

 position of equilibrium is independent of the viscosity of the liquid, but 

 the stability, t. e. the impulse necessary to carry the particle out of the- 

 cup, is increased with increase of viscosity. 



