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Dr. C. V. Burton on the 



occur if we could start from a condition in which each of the 

 border molecules, A, B, C, D, &c, had on the whole no charge ; 

 a condition, that is, in which the outer particles of each 

 molecule had a charge equal and opposite to the fixed charge 



Fig. 3. 



of the central particle. (We have already seen that this 

 is true for the average molecule within a homogeneous metallic 

 mass.) Now when B and C come into collision, it is evident 

 that the outer particles of B will lose some of their negative 

 electrification, while the outer particles of C will lose some of 

 their positive; and thus we see that when the distribution 

 of conduction-potential has become steady, such border par- 

 ticles as B or C will have on their outer particles a (negative 

 or positive) charge less than the (positive or negative) fixed 

 central charge, and to a smaller extent the same will be true 

 of particles (such as A, D, &c.) more remote from the border. 

 But when the settled condition has been reached, the passage 

 (say) of B backwards and forwards between A and C will not 

 change the distribution of charges amongst the molecules ; 

 and the condition that no change of the kind shall take place 

 is that when two molecules are in a position to collide their 

 conduction-potentials shall be equal. Now when B approaches 

 C (which has on the whole a negative charge) its potential 

 is lowered, and when B returns towards A its potential rises 

 again, so that if B in its backward and forward motion is not 

 to act as a systematic carrier of electrification between A and 

 C, the conduction-potential of A. must be higher than that of C. 

 Similarly, by considering C as moving backwards and for- 

 wards between B and D, we can see that B must have a 

 higher conduction-potential than D. 



This gives us a contact-difference of conduction-potential. 



If we suppose our analysis to become a trifle less pene- 

 trating, such molecules as B (and to a less extent A, &c.) will 

 appear to be positively electrified, C, D, &c. will appear to be 

 negatively electrified, and molecules farther removed from 

 the border will appear unelectrified. With still less micro- 



