CHAPTER IV. 



THE ARC IN AIR WITH PRESSURES GREATER OR LESS 

 THAN ONE ATMOSPHERE. 



Pressures Greater than One Atmosphere. But few 

 experiments have been performed with the arc in a gas 

 under pressure. Wilson and Fitzgerald 1 found that with 

 pressures greater than one atmosphere fumes of NO 2 were 

 formed and that these became very plentiful when the 



2 4 6 8 10 12 



ATMOSPHERES 

 FIG. 18. 



pressure was as great as 100 pounds per square inch. 

 Duncan, Rowland and Todd 2 found that the apparent re- 

 sistance of the arc increased as the pressure was increased, 

 as is shown in Fig. 18. The curves in this give the voltage 



1 Proc. Roy. Soc., 60, 377; 1896. 



2 Elektrot. ZS., 14, 603; 1893. 



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