column and other phenomena connected with the discharge. 313 



of the tube as it is much more noticeable in narrower tubes, 

 while in tubes exceeding 25 mm. diameter it was not observed 

 at all. 



The general effect of change of pressure is the same in 

 nitrogen and air as in hydrogen. In these gases, however, as 

 an increase in current never causes a decrease in distance between 

 the striae, their distance apart is never less for large currents 

 than for small ones ; hence at low pressures the corresponding 

 curves do not cross each other but merely become merged into 

 one. The decrease in distance, due to the sides of the tube, is 

 rather more marked than in hydrogen, and it occurs at a lower 

 pressure. 



From the results of numerous measurements it seems certain 

 that Goldstein's law, already stated, may be replaced more 

 accurately by the following : — If the striae do not reach to the 

 sides of the tube, then, for the same intensity of current, their 

 distance apart varies inversely as the pressure. 



Influence of the nature of the gas. 



8. The distance between the striae in different gases under 

 the same conditions of current and pressure is not very different ; 

 it bears no simple ratio to the density. At pressures between 

 1 mm. and "5 mm. they are further apart in hydrogen than in 

 nitrogen and air, for the two last gases the separation is the 

 same. The rate at which the distance between successive striae 

 decreases as the pressure increases is much greater in the dense 

 gases, and is greater in wide tubes than in narrow ones. If the 

 rates of decrease for hydrogen and nitrogen be compared it is 

 found that their ratio is independent of the diameter of the 

 tube and is equal to ^ nearly. From this it follows that if striae 

 could be obtained in nitrogen over the same range of pressure 

 as in hydrogen, then at the higher pressures the distance apart 

 would be appreciably greater in hydrogen. 



Influence of the diameter of the tube. 



9. The striae are further apart the wider the tube, but the 

 distance between bears no simple relation to the diameter or 

 section of the latter. Goldstein's second law (loc. cit.), viz. " That 

 if d is the distance between the striae then the ratio of the two 

 values of d at two given pressures is the same for all tubes," is 

 very approximately true when, as Goldstein says, the discharge 

 reaches to the sides of the tube, but does not hold Avhen the 

 distance between the striae varies inversely as the pressure ; in 

 this case the ratio is greater for wide tubes than for narrow ones. 



