338 [Dec. 18, 



discharges are consequently identical, and only differ in their appear- 

 ance according to the media through which they are passed. 



20. In a former communication to the Royal Society*, I have 

 also shown that the stratified discharge can be obtained by a single 

 disruption of the primary current of an inductive coil, however long 

 may be the vacuum-tube through which the discharge is passed. If 

 no addition is made to the battery with which the primary wire of 

 the apparatus is connected, or no alteration is made in the arrange- 

 ment of the coil, so as to increase or diminish the intensity of the 

 discharge, the stratifications will always present the same appearance 

 and form, occupying the same spaces and positions in the vacuum- 

 tube ; but if any change is made so as to alter the intensity, then a 

 corresponding alteration will appear in the discharge, the strict 

 assuming a different shape, and the bright and dark divisions 

 occupying different positions. 



21. When a galvanometer, a vacuum-tube, arid a solution of 

 iodide of potassium are arranged so as to form a continuous circuit 

 with the secondary coil of an inductive coil, not only is a luminous 

 stratified discharge produced, but the needle of the galvanometer 

 will be deflected, and iodine will be evolved by the induced momen- 

 tary action ; we thus obtain in this discharge all the indications and 

 conditions of a true voltaic circuit. 



In the continuous discharge of the battery we have the same 

 indications as that of the momentary current of the closed circuit of 

 an induction coil, and neither is resolvable by the rotating mirror. 



The stratified discharge from a single disruption of the primary 

 wire of the induction coil, and the continuous discharge of the voltaic 

 battery, are therefore identical in their character. 



22. With these preliminary observations, I now propose to ex- 

 amine the results obtained from the discharge of an extended series 

 of the voltaic battery in vacua described in this communication. 



1st. No. 248. The discharge under certain conditions is continuous, 

 and under other conditions it becomes intermittent. These conditions 

 are, that without any resistance introduced in the circuit, except that 

 inherent in the battery, the discharge cannot be resolved by the 

 rotating mirror, and so far may be considered as continuous ; but 

 when a certain given and described resistance is introduced in the 

 * Phil. Trans. 1858, p. 9, sect. 30. 



