642 
MESSRS. W. SPOTTISWOODE AND J. FLETCHER MOULTON 
C. The time occupied by positive electricity in passing along the tube. 
The time occupied by negative electricity in passing along the tube. 
D. The time occupied by positive discharge. 
The time required for the formation of positive luminosity at the seat of 
positive discharge. 
The time required for the formation of the blank space at the seat of 
negative discharge. 
E. The time occupied by either electricity in passing along a wire of the 
length of the tube. 
The period occupied by the whole discharge must be of the order B, since it 
includes a complete negative discharge. The evidence which shows that the time- 
quantities in D are greater than the time-quantity in E is much weaker than in any 
of the other cases, but this defect is not of great importance, as there would be little 
information to be derived from a comparison of them on account of them difference in 
nature. 
XXVII .—General conclusions as to the electric discharge. 
II. In vacuum discharges the durational character of the negative as compared with 
the positive discharge increases with the degree of exhaustion and becomes very 
marked in extremely high exhausts. 
We have seen in the previous section that the negative discharge occupies a longer 
time than the positive in leaving a terminal, whether that terminal be one that is 
formed on the glass by relief or special action or be an effective terminal of the tube. 
In the case of the positive discharge the time occupied is less than that required for 
electricity to pass along the tube ; while in the case of negative electricity it is longer 
than the time required by the comparatively slow-going molecules to do so, and is so 
much longer than the time required by the electricity to pass along the tube that a 
revocation caused by the arrival of the electricity at a spot near the other end of the 
tube is to all appearances in time to stop the negative discharge and its accompanying 
molecular streams before they have fairly commenced. In the present section we pro¬ 
pose to show that this durational character of the negative discharge, as contrasted 
with the positive discharge, increases with the degree of exhaustion of the tube, and 
becomes very marked in high exhausts.* 
It may fairly be remarked that the experiments upon which the proof of this com¬ 
paratively durational character of the negative discharge was based w r ere made in 
* This character of the negative discharge was already noticed by Messrs. De La Rue and Muller, see 
their paper, Phil. Trans., Part I., Yol. 169, p. 90, and also p. 118, where some very interesting details are 
given. 
