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VI. On the Sensitive State of Electrical Discharges through Rarefied Gases. 
By William Spottiswoode, D.C.L., LL.D., Pres. R.S., and J. Fletcher Moulton, 
late Fellow of Christ’s College, Cambridge. 
Received April 2,—Read May 8, 1879. 
[Plates 15-20.] 
Contents. 
Page. 
I. —Definition and description of the sensitive state .. .. 166 
II. —The sensitive state is due to a periodic intermittence in the discharge of considerable 
rapidity and regularity, the quantity of electricity in each individual discharge being 
sufficiently small to permit the discharge to be instantaneous. 167 
III. —The effect produced on a sensitive discharge by the approach of a conductor, is directly 
due to the relief given by its presence to the instantaneous electric tension within and 
around the tube, caused by the individual discharges in their passage through the tube 177 
IV. —The relief-effect (when the intermittence is effected near the positive terminal) 
assumes the form either of repulsion or of discharge from the interior surface of the glass. 
These two effects are identical in nature, and the form actually assumed depends, in the 
same tube, solely on the intensity of the action which calls it forth. 182 
V. —On the special or non-relief effects produced on the sensitive luminous discharge by 
connecting it with the air-spark terminal. 186 
VI. —On the nature of the electrical actions by which the relief and non-relief effects are 
respectively caused or accompanied. 188 
VII. —Examination and interpretation of the special or non-relief-effect when the positive is 
the air-spark terminal . 190 
VIII. —Examination and interpretation of special and relief effects in general in the case of 
interrupted discharges . 192 
IX. -—On the nature of striae, and the artificial production of striation in the luminous 
(sensitive) discharge. 199 
X. —The passage of the discharge through the tube occupies a time which is sufficiently 
small in comparison with the interval between the discharges to prevent any interference 
between successive electrical pulses.. 206 
XI. —The discharge is effected under ordinary circumstances by the passage through the tube 
from the air-spark terminal of free electricity of the same name as the electricity at 
that terminal. 209 
XII. —On unipolar discharges . 214 
XIII. —On the state of the tube during the occurrence of the discharge. 217 
Concluding remarks . 221 
Postscript— 
A. —On the variations of form of the negative glow.. 226 
B. —On the double character of the coil discharge . 227 
C. —On the intei'ference of intermittent discharges. 228 
