Striated Electrical Discharge. 525 



large. In other words, as we pass over the striations, moving 

 towards the cathode, two adjacent curves will tend to approxi- 

 mate more and more closely with every stria passed over, 

 until they may, by the time the cathode is reached, be 

 indistinguishable. 



The argument is reversible; two groups which are ex- 

 tremely close to one another at the cathode may diverge as 

 we pass away from the cathode (the divergence increasing 

 approximately in geometrical progression with every stria) 

 until by the time the anodes of the two graphs are reached 

 we have a divergence sufficient to give materially different 

 values for the distance between the electrodes, the total fall 

 of potential, &c. 



§ 14. Hence, if the distance between the electrodes or the 

 potential-difference between them be altered, the graph will 

 tend to adjust itself at the anode rather than at the cathode. 

 If there is, for any reason, a tendency for the discharge to 

 take a certain form at the cathode, it will be possible for the 

 discharge to approximate very closely to this form without 

 using up any of the disposable constants of the graph, while 

 the same is not true of the anode. The nature of the dis- 

 charge near the cathode may therefore reasonably be expected 

 to depend principally upon the physical conditions which 

 obtain at the cathode, while the discharge at the anode will 

 depend less upon the state of the anode than upon the 

 distance and potential-difference between the two electrodes. 



§ 15. These considerations seem to suggest an explanation 

 of the observed constancy in the appearance at the cathode, 

 as well as of certain other experimental results. For 

 instance, Sir W. Crookes, using as cathode a metal electrode 

 one-half of which was coated with lampblack, found that the 

 dark space opposite the lampblack was longer than that 

 opposite the metal, showing the dependence of the negative 

 discharge upon the state of the cathode *. At the same 

 time he found that the appearance of the negative end of the 

 discharge was independent of the position of the anode f. 



Goldstein, using two movable electrodes, observed that 

 whichever electrode was moved, the striaa and the negative 

 dark space behaved as though they were rigidly connected 

 with the cathode J. 



§ 16. Let us now try to form some conception of the state 

 of things which must, upon our theory, occur in a vacuum- 



* Crookes, Phil. Trans. 1879, p. 137, § 491. 

 t Loc. eit. § 489. 



X Wied. Ann. xii. p. 273. In this connexion see also Graham, VVied. 

 Ann. lxiv. p. 71. 



