MRS, H. AYRTON ON THE MECHANISM OF THE ELECTRIC ARC. 
327 
Table V.—Ratios of Mean Cross-Sections of Mist taken from Table III. 
Length of Arc, 2 millims. 
Ratios of Mean 
Cross-Sections, 
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) 
(4) 
(5) 
(6) 
(7) 
(8) 
(9) 
(10) 
4 to 6 
1-5 
2-04 
1-2 
1-51 
1-7 
1-98 
1-21 
1-56 
1-06 
6 „ 8 
1-33 
1-65 
1-71 
1-82 
1-6 
1-8 
1 • 33 
1-98 
1-04 
8 ,, 10 
1-25 
1-44 
1-46 
1-23 
1 ■ 33 
1 • 33 
1-34 
1-70 
1-25 
10 „ 12 
1-20 
1-49 
1-33 
1-31 
1-39 
1 ■ 46 
1-30 
1-48 
1-40 
12 „ 14 
1-17 
1-18 
1-25 
1-38 
1 -21 
1-43 
— 
1-13 
The most important point to observe in these tables is whether 8V 0 /SA is negative 
or positive with each set of carbons, i.e., whether the cross-section ratios are greater 
or less than the current ratios. Take first the non-normal ratios. When the positive 
carbon alone is cored, the sign of 8V C /SA is decidedly negative, just as it is when both 
carbons are solid, for all the cross-section ratios in column (9) of both Tables V. 
and VI. are greater than the corresponding current ratios in column (2). Moreover, 
with this particular length of arc, and these currents, the non-normal value of SV ( ./SA 
does not appear to be altered by coring the 'positive carbon alone, for the non-normal 
cross-section ratios in column (9) of each table are in some cases greater and in others 
less than those in column (7). When the negative carbon alone is cored, the non¬ 
normal value of SYrjSA appears to be negative, but approaching the zero point; for 
in Table V., one cross-section ratio in column (8) is less than the corresponding 
current ratio, one is equal, and three are greater; while in Table VI., three are less 
and two are greater. When both carbons are cored, the non-normal value of 8V e ./SA 
is positive; for three out of the five of the numbers in column (10) of Table V., and 
the whole of those in the same column of Table VI. are greater than the corresponding 
numbers in column (2). 
