1862.] 339 



circuit, the discharge becomes intermittent; with an increased re- 

 sistance the number of discharges in any given time is reduced, the 

 duration of such intermittent discharges being distinctly resolvable 

 by the rotation or vibration of the plane of a mirror in which they 

 can be reflected. 



2nd. No. 70. In this very imperfect vacuum, containing vapour of 

 iodine, the battery does not elicit any striae, but by the revolving 

 mirror the discharge is found to be intermittent. With the induction 

 coil the discharge in this tube elicits clearly defined but very narrow 

 striae ; from the coil we have a discharge of high intensity which 

 elicits stratifications, although they are not attainable by the lower 

 intensity of the battery. 



3rd. No. 319. We obtain evidence of two distinct states of a dis- 

 charge, of colour in the striae, and, under certain conditions, of 

 sound. 



4th. In No. 320 we have experimental proof that in the more 

 perfect vacuum the discharge will not pass, confirming my former 

 result obtained with the coil (Phil. Trans. 1859, p. 156),*that the 

 presence of a certain amount of matter is indispensable, and that 

 during the discharge heat is developed. 



5th. In No. 315, under all conditions of resistance described, the 

 discharge of the battery is stratified, but cannot be resolved by the 

 revolving mirror : in this tube we are enabled to determine and 

 regulate the number of striae, to some extent alter their colour, to 

 fix and determine their position, separating or closing up the dark 

 space between the luminous disks, these changes being entirely due 

 to the amount of resistance introduced in the circuit. 



The form, or figuration of the striae, and the positions they occupy 

 in the vacuum-tube, appear by these experiments to depend upon two 

 separate and distinct conditions : 



1st. The power or energy of the battery. 



2nd. The state of tension of the highly attenuated matter through 

 which the discharge is visible. 



The striae can be controlled, their number increased or reduced, and 

 their places or positions in the tubes altered by the introduction of 

 measurable amount of resistance in the circuit ; and thus they appear 

 to indicate the amount of force of tension which exists in a closed 

 circuit of the battery, as the divergence of the gold leaves of an 



