1894.] On some Phenomena in Vacuum-tubes. 241 



result follows. The object of this experiment was to see whether the 

 glass disk would set up its own bands independently of those due to 

 the rod, but the rod appears to gain the mastery. Probably the two 

 bands formed by the glass disk are driven (or repelled) into one by 

 the rod. 



Experiment 6. 



I next tried the effect of contractions to see whether the same 

 result would not be produced as if the deflector rod were employed. 

 Several forms of tubes are used : in some cases a little glass sphere, 

 as described in the previous experiment, without the rod attached to 

 it ; in other cases the tube was contracted for a definite length and then 

 expanded ; in other cases disks of glass and of mica were inserted with 

 holes in the centre, as shown in figs. 6, GA, and 6s. The same results 

 are produced as with the rod ; the distance of the bright bands apart 

 being equal, in the first tube, to the distance between the holes in the 

 glass sphere and its electrode ; in the second tube, to the length of 

 the contracted tube ; and in the third tube, to the distance between 

 the holes in the disk and its nearest electrode. 



When a tube, containing a glass or mica screen with a hole in it, is 

 employed, one of the three effects may be produced : 



1. Broad bands throughout the tube, as already mentioned. 



2. Very narrow bands, their distance apart being equal to the 

 distance between the two bright bands formed on both sides of the 

 screen in the tube. 



3. N"o bands in the tube, or only a confusion of bands, and no 

 distinct bands on either side of the disk. Unless this circumstance 

 were pointed out, it might prove misleading to anyone trying the 

 experiment. I tried a large number of tubes built up in this manner, 

 in order to discover the cause of the different phenomena. 



It would appear that broad bands are produced when the distance 

 between the disk and its nearest electrode is suitably adjusted. If 

 the screen is placed far away from the electrode, bands are produced 

 on each side of the disk, and they are reproduced throughout the 

 tube. If the screen is placed nearer to its electrode, the two disks 

 appear to be driven into one, and broad bands are produced. If the 

 screen is placed still nearer to the electrode, then what should be the 

 two bands on either side of the disk are driven through the hole, and 

 appear as a hemisphere of light on the side of the tube which is the 

 longest. In this case bands may or may not be produced, and, if 

 present, they are irregular. 



These three effects can be produced by varying the current in many 

 instances, and very probably in all cases ; but, as a rule, the tubes 

 break down before all the effects can be shown. 



Again, plain tubes are employed with electrodes of varying lengths. 



VOL. LVI. P. 



