296 Mr. A. P. Chattock on the Electrification 



again. The character of the sparks was quite different too. 

 The one which formed the resistance was thin and sharply 

 defined, and spread out for a considerable distance over the 

 plate like a splash. The other was much brighter, straight, 

 and without any signs of a defined edge. 



While, however, the above is evidence of the existence of 

 surface-resistance at used points, the fact that the values of / 

 at beginning and end of discharge are practically identical 

 for a clean point for both positive and negative electricity, 

 may be regarded as showing that such resistance is either 

 very small or non-existent on points which have not been used 

 before. 



Atomic Charge. 



§ 6. Assuming, then, provisionally that cohesion in Grotthuss 

 chains is the sole cause of the resistance offered to discharge 

 at a clean point, and that gas atoms are consequently con- 

 cerned in carrying the electricity when it does go*, there 

 arises the interesting question as to the amount of charge 

 carried by each atom ; and one is tempted to see whether 

 the above measurements throw any light on it. With- 

 out in any way pretending to settle the point, the following 

 considerations seem to me to render it probable that the 

 electrochemical equivalent of gas atoms is of the same order 

 of magnitude as that of the same atoms in electrolytes. 



The essence of a Grotthuss chain is that it shall consist of 

 molecules capable of being split into two parts, one of which 

 is charged after the split with positive electricity and the 

 other with negative. These charges may exist separately in 

 the molecules to start with, or they may be induced by an 

 electrostatic field — but in either case it is the field which 

 subsequently arranges them in chains ; and the breaking 

 down of the chains occurs when the mechanical pull of the 

 field on the charged parts is sufficient to overcome their 

 mutual affinity. This affinity may be due to one of two causes 

 or their combination. Either it is (a) the electrical attraction 

 of two initial charges, or it is (b) a cohesive attraction without 

 any previously existing charges, or it is (c) both. One of 

 these three it must be, if by cohesive attraction is understood 

 the sum of all nonelectrical forces between the two parts of 

 the molecule. 



Consider the first (a) of these cases. If the molecules hold 



* This does not preclude the possibility of metal dust in the discharge 

 after it has once started. 



