306 Mr Willows, On the distance between the striae in the positive 



due could not be exactly determined ; two conditions however 

 seemed necessary, viz. that the gas should be damp and that the 

 electrodes should not have been used for some time previously. 

 The latter may possibly mean that the electrodes must contain 

 occluded gas. Thin electrodes were apparently better for their 

 production than thick ones. These fine striae did not always 

 appear even when these two conditions were fulfilled, showing 

 that they were not always sufficient, although they could be 

 proved necessary. Moist gas is certainly necessary, for they could 

 never be obtained when it was dry ; in fact, a tube which con- 

 tained moist air and was presenting the appearance described, 

 gave an entirely different appearance, and the striae several mm. 

 apart when it was put in communication with a bulb containing 

 P 2 5 for a few hours. As the current which passes through a tube 

 giving these narrow striae is increased the striae get brighter as 

 is the case in the normal state, but this increased brightness soon 

 gives place to a general haziness and as the current is further 

 increased the positive column becomes continuous, although with 

 dry air at the same pressure the striae would be quite distinct. 

 When the pressure was reduced the normal striations then ap- 

 peared, and when this had once taken place it was difficult to 

 again produce the first state; pumping out and refilling with 

 moist air frequently failed to do this, but if the tube was allowed 

 to stand open for some weeks and then exhausted the fine striae 

 generally reappeared. 



It is possible that when the air is moist a large part of the 

 current is conveyed by the water vapour and that the narrow 

 striae are those given by this ; it is well known that in a damp 

 gas conveying a discharge the hydrogen lines are present. 



If this be so, it is difficult to see why the admission of fresh 

 moist gas should fail to reproduce the appearance. 



The resistance of the tube to the passage of the discharge 

 was considerably diminished by drying the contained gas. 



This agrees with experiments of Bailie 1 and Warburg 2 , for at 

 these pressures a considerable fall of potential takes place along 

 the positive column and the latter observer found that moisture 

 increased the potential differences along this. 



5. De la Rue and Muller 3 in one of their papers on the 

 discharge produced by their large silver chloride battery give 

 numerous photographs of the striated discharge. Some of these 

 are remarkable in presenting a series of double striations. It 

 seemed to be of interest to see whether these were due to 



1 Annal. de Chimie et de Physique, 25, p. 486. 1882. 



2 Wied. Annal. 31, p. 545. 1887 ; 40, p. 1. 1890. 



3 Phil. Trans. 1878, Part i. p. 155 ; see also p. 112, Recent Researches. 



