328 
MRS. H. AYRTON ON THE MECHANISM OF THE ELECTRIC ARC. 
Table VI.—Ratios of Cross-Sections of Mist where it Touches the Crater, taken 
from Table IV. 
Length of Arc, 2 millims. 
Ratios of Cross-Sections at Crater. 
Change 
of 
Current. 
Current 
Ratios. 
Normal. 
Non-normal. 
S.S. 
S.C. 
C.S. 
C.C. 
S.S. 
S.C. 
C.S. 
C.C. 
(1) 
(2) 
(3) 
(V 
(V 
(6) 
(7) 
(8) 
(9) 
(10) 
4 to 6 
1 -50 
2-34 
1-07 
1-66 
2-00 
3-76 
0-80 
1-95 
1-24 
6 „ 8 
1-33 
2 • 35 
1-44 
2-05 
2-50 
2-35 
1-00 
2-06 
1-08 
8 „ 10 
1-25 
1-44 
2-00 
1-12 
1-47 
1-21 
1-29 
1-40 
1 05 
10 „ 12 
1-20 
1-41 
0-96 
1-44 
1-04 
1-37 
0-88 
1-44 
1-00 
12 „ 14 
1-17 
1-20 
1-44 
1-31 
1-09 
_ 
1-34 
— 
0-88 
Turning next to the normal ratios, we find that when the positive carbon alone is 
cored, SV ff /SA lias still much the same negative value as when both carbons are 
solid, since the numbers in column (5) differ on the whole very little from those in 
column (3). When, on the other hand, it is the negative carbon alone that is cored, 
there is a change, for instead of being a little below zero, SVySA is decidedly 
negative, since in Table V. all but one of the numbers in column (4), and in Table VI. 
all but two are greater than the corresponding numbers in column ( 2). When both 
carbons are cored, there is an even greater difference between the normal and non¬ 
normal values of SV r /SA. For in Table V. all the numbers in column (6), and in 
Table VI. all but two are greater than the corresponding current ratios, showing 
that SV ( ./8A is negative for normal changes of current though it is positive for 
non-normal changes with these carbons, currents, and length of arc. 
To sum up the change in the value of 8 VySA produced by coring one or both of 
the carbons, we find that while coring the positive carbon alone makes very little 
difference in either the normal or non-normal change of cross-section that accom¬ 
panies a given change of current, coring the negative carbon diminishes the change 
of cross-section, both for normal and non-normal changes of current, but more for 
the second than for the first, and more when both carbons are cored than when the 
negative alone is cored. Thus, coring the negative carbon both diminishes and 
retards the change in the cross-sections of the arc that accompany a change of 
current. This retardation of the change of cross-section is quite sufficient to account 
for the fact already mentioned on p. 311, viz., that if 1 quickly altered the resistance 
in the circuit outside the arc, when both carbons were cored , I could sometimes see 
