76 Royal Society : — 



An electro-magnet is placed at C, and is constructed so as to allow 

 the two helices to be separated ; and by these means the larger vessel 

 can, if required, be placed between them, and any portion of the 

 luminous discharge may be thus exposed to any part of the magnetic 

 field. 



"When the terminals of an excited induction coil are attached to 

 the wires of either of the above vacuum-tubes A or B, luminous 

 discharges are obtained, the negative wire ball or plate being 

 covered with a luminous cloud-like glow extending towards the 

 positive ; but the stratifications are not developed, except by the 

 magnet, and these become more clearly defined as the magnet is 

 caused to approach, or as the power is increased, when they are de- 

 flected according to the direction of the discharge, or of the polarity 

 of the magnet. But with the induction coil, no matter how I re- 

 duced the intensity of the discharge, or varied that of the electro- 

 magnet, in no instance could I produce in these, or in any of my 

 vacuum-tubes, a similar result to that which Mr. Grove obtained in 

 the vacuum-tube so unfortunately broken ; the experiment evidently 

 requires a certain balance of power between the electric discharge 

 and that of the magnet, and this I had hitherto been unsuccessful 

 in obtaining. 



I next experimented with my water-battery (Phil. Trans. 1844, 

 and Proceedings, 26 May, 1859), which I have recently had carefully 

 cleaned and recharged with rain-water ; the luminous discharge in 

 both the vacua A and B was obtained with less than 1 000 series, 

 and this discharge, as well as that from the full series of the battery of 

 3520 cells, was under certain conditions, hereafter described, entirely 

 destroyed or interrupted by the power of the magnet. 



At first the interruption or break in the luminous discharge ap- 

 peared to be caused by the sudden action of the magnet, as if it were 

 merely momentarily blown out, for the discharge recovered itself 

 while it remained under the influence of the magnet — the luminous 

 discharge under this condition gradually reappearing stratified and 

 strongly deflected j but I subsequently ascertained that, by carefully 

 adjusting the intensity of the battery discharge, and the force or power 

 of the electro-magnet, this recovery in the discharge could be en- 

 tirely prevented. 



On approaching the vacuum A towards the electro-magnet, the 

 luminous discharge from the battery assumed the same form as that 

 from the induction coil ; but when the vacuum was placed between 

 the helices, so as to permit the armatures or poles of the magnet 

 to touch one or each side of the glass vessel at about its centre, the 

 discharge disappeared ; as soon as the magnet was removed, or the 

 vacuum-tube withdrawn from its influence, the luminous discharge 

 was reproduced. 



To test whether a complete disruption of the electrical current 

 had taken place, two gold-leaf electroscopes were attached, one to the 

 zinc and the other to the copper terminal of the water-battery ; the 

 leaves diverged with considerable energy ; connection was then made 

 from the electroscopes to the wires of the vacuum-tube ; the luminous 



