Mr. W. Spottiswoode on Stratified Discharges. 147 



acid tube with the slit attached. This tube, viewed by the eye, 

 shows flake-like fluttering striae, with a slight tendency to floccu- 

 lency near the head of the column. The commencement of the 

 discharge is at the right hand, and the negative terminal at the 

 top. The drawing fairly represents the appearance of the upper 

 part or head of the column of striae during one complete coil-dis- 

 charge. When the battery-surface exposed is small, the whole 

 consists of, first, three or four columns of striae of decreasing 

 length, and afterwards of an almost unbroken field of strice. Each 

 of the initial columns is perfectly stratified ; and the same disposi- 

 tion of striae prevails throughout the entire discharge. The striae 

 which fill the main part of the field present a proper motion 

 nearly uniform, but slightly diminishing towards the end. These 

 striae are for the most part unbroken, but are occasionally inter- 

 rupted at apparently irregular intervals. When the battery-sur- 

 face is increased the elementary striae are more broken, and near 

 the head of the column the interruptions occur as in the figure. 

 The separation of the earlier part of the discharged into striated 

 columns divided by intervening rifts does not, with the exception 

 of the first, extend far towards the positive terminal. Neverthe- 

 less, even as far as the positive terminal itself, there seems at 

 times to be a fuller development of discharge than is subsequently 

 maintained. 



The first rift in the discharge, following the first outburst, is 

 sometimes distinguishable even, as far as the positive terminal, 

 and, perhaps, in those cases indicates a real cessation of the dis- 

 charge. This is corroborated by the fact that a similar interrup- 

 tion is then perceptible in the glow surrounding the negative ter- 

 minal ; but after this the negative glow retains its unbroken cha- 

 racter throughout the entire period of the discharge. 



The stratified columns with their intervening rifts are some- 

 times reproduced towards the close of the discharge ; but this ap- 

 pears to take place only when the battery is in an unusual con- 

 dition of energy, and disappears when, as in the bichromate bat- 

 tery, polarization of the plates rapidly takes place. On these oc- 

 casions especially, but also at other times, traces may be seen of 

 the faint lines of light connecting the positive with the negative 

 parts of the discharge mentioned by Wiillner in the paper quoted 

 above. 



Other tubes, when viewed by the eye, show flaky striae more 

 or less difficult to distinguish from one another. Observed in the 

 mirror, they show much the same phenomena as the tube figured 

 above, except that the striae are rather more crowded together 

 and slightly more broken. This is the case especially with am- 

 monia-tubes, in some of which the striae are undistinguishable by 

 the eye,, and which accordingly give the impression of an unstrati- 

 fied column of light. 



!Fig. 2 represents the appearance in the mirror of another car- 

 bonic-acid tube with a current similar to that used in the former 

 case. Viewed by the eye it shows flocculent striae, each having a 

 contour sharply defined towards the negative terminal, loosely de- 



L 2 



