118 DR. W. (1 DUFFIELD, MESSRS. THOS. H. BURNHAM AND A. H. DAVIS ON 



any outstanding effect which might be due to these influences was specially looked 

 for by using two vertical arcs, but it was found to be inappreciable. 



Fig. 9. 



Tables VII. and . VIIT. give the means of a large number of observations obtained 

 by this method. 



TABLE VII. (DAVIS). Direct Current. Variation of Total Pressure with 



Current and Arc-length. 



TABLE VIII. (DAVIS). Total Pressures for a Current of 6 Amperes. 

 Variation with Arc-length. 



In this table mean values only are given. Fig. 12 shows the individual readings. 



