MRS. H. AYRTON ON THE MECHANISM OF THE ELECTRIC ARC. 
323 
Table IV.—Cross-section of Mist where it touches Crater, with -f Solid — Solid, 
+ Solid — Cored, + Cored — Solid, + Cored — Cored Carbons. 
Apostle Carbons, 11 millims. and 9 millims. 
Length of Arc, 2 millims. 
Current in 
Normal. 
Non-normal. 
Amperes. 
(1) 
(2) 
(3) 
D) 
V) 
(6) 
(D 
(8) 
S.S. 
S.C. 
C.S. 
c.c. 
S.S. 
S.C. 
C.S. 
C.C. 
4 
2-9 
7-8 
3-2 
2-9 
6 
G • 8 
9-0 
5-3 
5 • S 
10-9 
G • 25 
G-25 
3-6 
8 
16-0 
13-0 
10-9 
14-4 
1G-0 
9-0 
10-9 
G-25 
10 
23-0 
26-0 
12-25 
21-2 
19-4 
1G-8 
15-2 
15-2 
12 
32-5 
25-0 
17-6 
22-1 
31-4 
23-0 
17-6 
21-2 
14 
39-1 
36-0 
23-0 
24-0 
— 
33-6 
— 
19-4 
Thus, taking Tables III. and IV. together, we find that a core in the positive 
carbon keeps both the mist and the vapour film from being as large as they would be 
with a solid positive, both immediately after a change of current and when the arc is 
normal again. Coring the negative, on the other hand, while it has the same effect 
on the cross-section of the mist as coring the positive, only diminishes the cross- 
section of the vapour Jilin immediately after a change of current. If, therefore; 
coring either carbon produced nothing but an alteration in the cross-section of the 
arc, the resistance of the arc, and, consequently, the P.D. between the carbons would 
be increased by the coring. It follows, therefore, that the diminution of the P.D. 
between the carbons actually observed with cored carbons must be caused by a 
lowering of the specific resistance of the vapour film or of the mist, or of both; and 
this lowering must be so great that it must more than compensate for the diminution 
in their cross-sections. 
It is easy to see how r the vapour and mist from a core in the positive carbon must 
alter the specific resistance of the arc, but, since the negative carbon does not 
volatilise, there seems to be no reason why coring it should have the same effect. 
The core, however, consists of a mixture of carbon and metallic salts; and metallic 
salts have a lower temperature of Volatilisation than carbon, so that these salts may 
easily be volatilised by the mist touching them, and, mingling with it, lower its 
specific resistance. 
Now take the fact that, with a constant length of arc, on increasing the current the 
P.D. always diminishes less if the positive carbon is cored than if it is solid, and that 
the reduction of diminution is sometimes so great that the P.D. remains constant for 
a large increase of current, and sometimes even increases somewhat, instead of steadily 
diminishing, as it does when both carbons are solid. 
2 T 2 
