358 M. E. Goldstein on Electric Discharges 



14. The stratification of the positive discharge shows a con- 

 tinuous variation of forms^ the first and last of which have 

 little resemblance to each other. One extreme form repre- 

 sents the stratification as it was first observed, and which is 

 generally known: it consists of a series of narrow disks of 

 light separated by small and dark intervals. The other ex- 

 treme form shows long columns of light, the length of which 

 is sometimes a hundred times that of the former kind ; these 

 long columns follow each other closely : the beginning of 

 one and end of the other is chiefly marked by the fact that 

 the different poles of one stratification have a different in- 

 tensity. 



The two kinds of stratification may appear in the same tube. 

 The first kind corresponds to the pressure at which the strati- 

 fication first appears on exhausting the tube ; the other form 

 corresponds to the lowest pressures at which the stratification 

 is still visible. Difterent gases show also variations in the form 

 of the stratification which first appear on exhausting the tube. 



15. The brio-htness of each stratification is not uniform. It 

 has a maximum at its negative pole and decreases towards 

 the positive pole, quickly if the length is small, more slowly if 

 the stratification is long. 



16. Besides the unsymmetrical distribution of brightness, 

 one and the same stratification shows sometimes difterences in 

 colour. These differences are sometimes not only difierences 

 in tint merely, but two colours which stand in strong contrast 

 to each other may succeed each other — for instance, red and 

 blue or yellow and blue. One stratification may even show 

 more than two colours. 



A variation in pressure causes a variation in the colour of the 

 stratification. The changes are more or less striking, according 

 to the nature of the gas. Hydrogen, for instance, which was pre- 

 pared by means of zinc and sulphuric acid and purified in the 

 usual way, though not absolutely without odour, showed suc- 

 cessively the following colours in one stratification as the tube 

 was exhausted : — first, half blue and half pink ; then entirely 

 blue; then half yellow and half blue; then entirely grey. 

 The length of the stratification, was about 1^ to 2J centims. 

 If the hydrogen was readmitted and then exhausted again, 

 the same variations reappeared in the same order. 



17. A closer study of the behaviour of stratification leads 

 to the conclusion, that the various positive stratifications which 

 appear simultaneously in a tube which is of the same width 

 throughout are not equivalent. They difier from each other 

 in the same way, though not to the same degree, as so-called 

 positive light from the negative light. 



