90 Mr. W. Spottiswoode on Stratified Discharges. [Mar. 22, 



March 22, 1877. 



Dr. J. D ALTON HOOKER, C.B., President, in the Chair. 



The Presents received were laid on the table, and thanks ordered for 

 them. 



The following Papers were read : — 



I. "On Stratified Discharges. — IV. Stratified and Unstratified 

 Forms of the Jar-Discharge." By William Spottiswoode, 

 M.A., Treas.R.S. Received March 7, 1877. 



It is well known that if a Leyden jar be discharged through a vacumn- 

 tube, the discharge generally takes the form of an unbroken column of 

 light, extending from the point of the positive terminal to the hilt of the 

 negative, i. e. to the extreme negative end of the tube, and that it shows 

 no trace of either negative glow or intervening dark space. On the 

 other hand I have found, by experiments with a large Leyden battery, 

 that if a tube have one terminal connected with the negatively charged 

 coating of the battery and the other held beyond striking-distance from 

 the positively charged coating, the discharge in the tube will show a 

 separation of the positive from the negative part by a dark intervening 

 space. Under suitable circumstances of exhaustion it will also show 

 striae, in the same manner as when the discharge is effected directly with 

 a Holtz machine, having the conductors either closed or open beyond 

 striking-distance (see Roy. Soc. Proceedings, vol. xxiii. p. 460). Again, 

 I have found, with the same battery, that if the tube be connected 

 otherwise as before, and held at a distance less than at first, but a little 

 greater than striking-distance, a stratified discharge much more brilliant 

 and more like that produced by a coil will be exhibited. It should be 

 remarked that the latter form of discharge appears to the unassisted eye, 

 in the cases which I have examined, as an unbroken column of fight, but 

 with a negative glow and dark space. A revolving inirror, however, re- 

 solves the column into a regular array of striae, having a rapid proper 

 motion towards the positive terminal. 



The transition from the first to the second of these forms, and from 

 the second to the jar-discharge proper when the tube was brought within 

 striking-distance, was, if not absolutely abrupt, at all events so rapid 

 that this form of experiment gave no prospect of following one form 

 into the other. With a view to examining the transition as closely as 

 possible a Holtz machine was employed, and the jars having been taken 

 off:, a pair of mica plates partially covered with tinfoil was used in their 

 stead. By sliding one plate over the other, so that more or less of 



