1909] oil Electrical Striations. 583 



is reached after longer and longer intervals, and there is time to 

 observe the initial distribution of the electric field. 



We see that the result of the experiments with the cathode rays 

 is to confirm the indications of the wire detector, even when the 

 main current is travelling against the electric force. That the wires 

 in this case should indicate the potential is very remarkable, and 

 must be due I think to the presence in the discharge of slowly 

 moving ions in addition to the swiftly moving ones which carry the 

 main portion of the current, having acquired in other parts of the 

 field sufficient impetus to carry them for some distance against an 

 opposing electric force. The slowly moving ions would be produced 

 by the collisions of the quick ones, and those produced near the tips 

 of the wire electrodes would follow the lines of electric force near 

 the wire and equalize the potentials between the wire and the gas. 



The great change in the electric force which occurs at the bright 

 fronts of the striations shows that in these regions we have a great 

 accumulation of negative electricity, while the distribution of the 

 electric force in other parts of the striations and in the dark parts 

 between two striations shows that in those regions there is a slight 

 excess of positive electricity. The magnitude of the charges in the 

 electric force is shown by the following numbers, which indicate the 

 electric force in volts per centimetre at different parts of the 

 striation. x in the following table is the distance in millimetres 

 from the bright head of the striation : x is taken positive when mea- 

 sured towards the anode, negative towards the cathode, thus x = -1 

 denotes a place 1 millimetre from the bright head of the striation on 

 the cathode side. X is the electric force in volts per centimetre at x. 

 The gas was hydrogen at a low pressure. 



X X 



- -5 - 9 



+ -5 +67 



+ 1-5 +33 



+ 3-5 +30 



+ 7 +10 



+ 9 -10 



The last reading was at a point just in front of a second striation. 



The distance between the bright heads of successive striations was 

 9 mm. and the thickness of the dark space 2 mm. 



From the preceding table we see that in the space of 1 mm. at 

 the head of a striation we have a change in the electric force of 76 

 volts per cm. By means of the equation 



^X , 

 dx 



Vol. XIX. (No. 103) 



