PRESSURES GREATER OR LESS THAN ONE ATMOSPHERE 79 



taken with a current of 10 amperes and a distance of 

 2 mm. between solid carbons. 1 



3 4 



LENGTH IN MM. 



FlG. 24. 



A more extended examination of the arc in a vacuum 

 has been made by Hoerburger. 2 His results are shown in 

 Figs. 23 and 24. The first gives the relation between volt- 

 age and pressure of the gas for different lengths of the arc, 

 the current being 6 amperes. Fig. 24 shows the relation 



1 As has been shown in Fig. 18, Duncan, Rowland and Todd found 

 with longer arcs an increase in voltage when the pressure was reduced 

 below one atmosphere. This, however, is contrary to the observations of 

 all other experimenters. 



2 Dissertation Griesswald. Beib., 29, 883; 1905. 



