118 DR. W. G. DITFFIELD, MESSRS. THOS. H. BURNHAM AND A. H. DAVIS ON 
any outstanding effect which might be cine to these influences was specially looked 
for by using two vertical arcs, but it was found to be inappreciable. 
Tables VII. and VIII. 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. 
Total pressure upon anode in d_vnes. 
Current in 
amperes 
2 -5 
3 
4 
5 
G 
7 
8 
9 
10 
2 -5 
3 
4 
5 
0 
7 
8 
9 
10 
Arc- 
length. 
mm. 
1 
0 -15 
0-26 
0 -52 
0-70 
1 T6 
2 
0-13 
0 -21 
0-51 
0-75 
0 -90 
0 -98 
1 -24 
1 -63 
2 -07 
0 -03 
0-05 
0 -18 
0 -32 
0 -46 
0 -85 
1 -03 
1 -16 
1 -75 
„ r Set A 
0 09 
0 -39 
0-37 
0 '04 
0-78 
1 17 
1 -54 
1 -72 
0-08 
0 -13 
0 -23 
0 -.39 
0 -39 
0 -71 
0 -74 
1 -20 
1 Set B 
0 -03 
0-24 
0 -39 
0 -51 
0 -61 
0 -86 
1 T2 
1 '58 
5 
0 -34 
0 -65 
0 -81 
0 -87 
1 -21 
1 -47 
1 -55 
0 -23 
0 -31 
0 -41 
0 -.59 
o 
o 
0-98 
1 -15 
7 
0 -52 
0-7o 
0 -90 
0 -90 
1 -21 
1 -42 
2-02 
Total pressure upon cathode in dynes. 
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. 
