318 
MRS. H. AYRTON ON THE MECHANISM OF THE ELECTRIC ARC. 
Ray and Watlington, two students at the Central Technical College, in continua¬ 
tion of the researches of Messrs. Frith and Rodgers. The carbons were solid, and 
the direct current normal arc carried a current of 10 amperes with a P.D. of 45 
volts. Simultaneous values of the current and P. D. were taken with the Joubert 
point by point method. Some of these are given in Table II., in which the columns 
headed V,- are the P.D.’s with increasing currents, and those headed Y d with 
diminishing currents ; while V, and V/ belong to the smallest and largest current 
respectively. 
It may be seen at a glance that in every single instance the P.D. for the same 
current is higher when the current is increasing than when it is diminishing. For 
instance, with the lower frequency the P.D. corresponding with a current of 11 
amperes is 42’4 volts when the current is increasing, and only 41’8 volts when it is 
diminishing. And with the higher frequency it is 43‘2 volts with increasing current, 
and only 42‘0 with a falling current. Hence, we are supplied with a very simple 
test as to whether the superimposed alternating current changes the resistance of the 
arc or not. It is only necessary to take the wave form of P.D. and current by means 
of an oscillograph, and to observe whether the P.D. corresponding with each current 
is the same with increasing as with diminishing currents. If the two P.Ds. are 
different, the resistance is being altered, if they are alike, it is not. 
Table II.—Instantaneous Values of Corresponding Currents and P.Ds. with Small 
Alternating Current Superimposed on Direct Current of 10 Amperes in the Arc. 
P.D. with Direct Current alone, 45 volts. 
Solid Apostle Carbons : Positive, 11 millims. ; N egative, 9 millims. 
A. 
V. 
Frequency, 47. 
v s . 
Frequency, 115. 
V,. 
Vz. 
V,,-. 
A. 
Vi. 
V. 
V. 
8-425 
45 • 6 
8-65 
4G 
9-0 
— 
44-8 
— 
. 44-0 
9-0 
— 
45 ■ 6 
— 
44-9 
9-5 
'- 
44-2 
— 
43-3 
9-5 
— 
45-2 
— 
44-2 
10-0 
— 
43-7 
— 
42-8 
10-0 
— 
44-6 
— 
43-5 
10-5 
— 
43-1 
— 
42-1 
10-5 
— 
43-9 
— 
42-9 
11-0 
— 
42-4 
— 
41-8 
11-0 
— 
43-2 
— 
42-0 
11-5 
— 
42-0 
— 
41-4 
11-25 
— 
— 
42-2 
— 
12-0 
— 
41-7 
— 
41-2 
— 
— 
— 
— 
— 
12*25 
— 
— 
41-4 
— 
-- 
— 
— 
— 
— 
