106 Mr. J. B. Peace. Potential Difference required [June 1(3, 



Fm. 3. 



These results, and the curves representing them, present two 

 features, already mentioned, which call for remark. In the first 

 place, the potential difference curves in fig. 2 exhibit minima at pres- 

 sures which are relatively high. The following table (p. 107) gives 

 the minima shown by the curves, as drawn in fig. 2. 



In every series of observations these minima were well marked, 

 and for different series the pressures corresponding to the minimum 

 potential difference for a given spark-length were always in close 

 agreement. These minima are considered again below, in connexion 

 with the results of Part II. 



In the second place, the potential difference curves in fig. 2 meet 



