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



always possible to get the striae in a steady condition over the 

 whole range of pressure in which they were visible when it was 

 attempted to use the same current throughout, so that four com- 

 plete series of readings could not always be obtained. 



Measurements could be obtained with hydrogen over a range 

 of about 10 mm. Starting at the highest pressure the striae 

 were further apart for greater currents but for pressures near 

 •5 mm. the reverse was true. This is what would be expected 

 from what has been said in the previous section concerning the 

 manner in which the pressure influences the amount of current 

 required to produce the maximum separation. Hence if the 

 observations be presented in the form of curves having distance 

 between striae for ordinates and pressures for abscissae, the 

 current being constant throughout one curve but different for 

 different curves, then each of these will cut the others. 



This is clearly shown in fig. 4. 



11 

 10 

 9 



£ 8 

 £7 



5 5 



•5 I 1-5 2 2-5 3 3-5 4 4-5 5 5-5 6 65 7 



PRESS. /N /yi.M. 



Fig. 4. Showing the relation between pressure and distance between striae 



in hydrogen. 



The numbers on the curves give the current in galvanometer 

 deflexions. 



It is seen from the figure that at a pressure of about a mm. 

 the striae get nearer together, and that shortly after this as the 

 pressure is decreased, they are the same distance apart for all 

 currents ; when this holds, the rate of variation with pressure is 

 much greater than it was before. 



This appears to be due to the controlling action of the sides 



