Discharge in a De La Rive's Tube. 505 



these points already. Experiments for farther elucidating 

 them are in progress. 



9. III. In the case of air, the curve connecting pressure 

 and potential difference between the electrodes consists of 

 four portions. The first portion, which is very nearly straight, 

 corresponds to the " spray " discharge. As the " spray " 

 discharge changes into the " band/' there is a bend in the 

 curve towards the line of pressure. The next portion is also 

 a straight line. Gradually, the curve bends away from the 

 line of pressure, meeting asymptotically the line of potential 

 difference. 



10. We have just seen that f(KeX)—y = Q during the 



band or rotatory stage, that is fl — I — y = 0, since X= -, 

 p being the pressure. \P / P 



If now 7 is constant, we have fl — J = constant, which 



shows that the curve connecting p and potential difference 

 will in this case be a straight line, if the spark-length is 

 constant (as is known to be the case, both on Paschen's 

 law and experimental grounds). 



If 7 is not constant, the curve will not be a straight line. 

 This may explain why, in the case of complex gases and 

 vapours, the curve is not a straight line. /Xe\ 



11. If/(Xg\)— yis negative, so that/ \^)~ V = ~ a ' sa 3 r > 



this will correspond to the (first) stage, during which cor- 

 puscles are decreasing as the result of collision and recom- 

 bination and tending to equality with positive ions [art. 5]. 



Assuming u to be constant and less than 7, we deduce that 

 the curve connecting p and potential difference corresponding 

 to this stage will also be a straight line, inclined at a greater 

 angle to the line of potential difference than the line corre- 

 sponding to the rotatory stage [art. 10]. 



This would explain the first bend in the curve [art. 9]. 



In the third stage of the discharge, the form of the curve 

 is consistent with the supposition that collisions are then few, 

 and 7 — ct rapidly decreases with pressure. 



12. It has been found from experiment that hydrogen 

 shows no rotation when the discharge is that due to an 

 induction-coil. This is obviously due to the fact that for 

 such a discharge, f(KeX) — 7 is never zero in the case of this 

 gas, or what is the same thing, a steady state of ionization 

 throughout the length of the discharge-tube cannot be 

 established under the conditions of the experiment. 



The peculiar behaviour of hydrogen in a vacuum-tube 

 generally would seem to be connected with this property. 



