THE PRESSURE UPON THE POLES OF THE ELECTRIC ARC. 
129 
Table X.— The Pressure upon the Poles of an Arc, 6 mm. long, carrying 10 amperes. 
Series. 
Figure. 
Observed 
total 
pressure 
in 
dynes. 
Con- 
vexion 
cor¬ 
rection. 
Dynes. 
Cor¬ 
rected 
pressure. 
Dynes. 
Mean 
corrected 
pressure. 
Current carried solely 
by electrons. 
Half-current carried 
by electrons. 
ejm. 
V. 
ejm. 
V. 
1 
. Cathode. 
B 
16 
1-60 
1-10 
2-70 
1 
B 
14 
0-54 
2-23 
^2-18 
6-4 X 10^ 
2-8X108 
1-6 X107 
1-4X108 
C 
14 
1-11 
0-50 
1-61 
J 
E.xM.U. 
cm./sec. 
E.M.U. 
cm.jsec. 
2, Anode. 
B 
15 
1-35 
0’52 
1-87 
1 
B 
15 
1-79* 
0-60 
2-42 
^2-10 
19-0 X 10' 
7-9 X108 
4-7 X107 
3-9X108 
C 
15 
1-68 
0-34 
2-02 
J 
The values for the observed pressures were taken from the diagrams named in column 2 by drawing 
a line through the points of observation and noting where it met the vertical axis, and this point taken 
as the origin. When the graph was not straight the tangent was drawn to touch the curves at 10 amperes 
and similarly treated. 
* Calculated for arc-length of 7 mm. 
Previous Investigation. 
In 1882 Dewar! measured the hydrostatic pressure within the arc by using 
hollow carbons connected to delicate water manometers and found that “ during the 
maintenance of the steady arc the manometer connected with the positive pole 
exhibited a fixed increase of pressure corresponding to 1 to 2 mm. of vertical 
water pressure in different experiments and under varied conditions. The mano¬ 
meter connected with the negative pole shows no increase of pressure, but rather, 
on the average, a diminution.” 
Dewar gives no data respecting current and arc-length, but we may note that the 
hydrostatic pressure near the anode is about one hundred times the total pressure 
upon the poles measured in the present research. 
Dewar suggests that the phenomenon is consistent with “ the well-defined 
boundary of the heated gases acting as if it had a small surface tension,” and he 
suggests as a possible cause “the motions of the gas particles under the conditions 
of transit of material from pole to pole or a succession of disruptive discharges.” 
t Dewar, ‘Roy. Soc. Proe.,’xxxiii., 262, 1882. 
