ELECTRIC DISCHARGE WITH THE CHLORIDE OF SILVER BATTERY. 
89 
As the pressure was diminished the arc widened out until at last the entire surface 
of the negative disc was covered with a luminous discharge. From the first it will be 
seen that the central spindle did not extend quite up to the negative, as shown in 
fig. 19, at atmospheric pressure; that in fig. 18 the central bright part detached 
itself so as to form an entity; in figs. 17, 16, and 15 distinct strata were formed; 
then that, as is shown in figs. 14 and 15, the central bright portion diminished, the 
dark discharge near the negative increasing; while at the lower pressures, represented 
in figs. 12 and 11, there existed no central spindle, and that with the exception of the 
luminosity on the terminals the rest of the discharge was dark. It should be men¬ 
tioned that part of the details have, in some instances, been supplied from sketches 
made when the photographs were obtained, for there was sometimes a movement in 
the discharge which produced a confused picture. No observations of the expansion 
of the gas were attempted. 
The appearance of the discharge in carbonic acid is shown twice the original size in 
Plate 10, figs. 20, 21, 22, and 23 ; in all but the last will be observed the peculiar 
bell-shape form which is characteristic of the arc in carbonic acid (Part I., page 96, 
3 of fig. 23). 
Fig. 
M. 
cells. 
20 
983,158 
10,960 
from a drawing. 
21 
504,211 
6300 
?? 
22 
126,052 
2400 
23 
39,474 
1200 
? J 5) 
In fig. 20 is seen a central spindle surrounded by a bell-shape fainter discharge ; in 
fig. 21 the central spindle is composed of well-defined strata; in fig. 22 there is a 
bright luminosity in contact with the positive disc, then a dark interval with an 
illumination of the negative surface, the whole surrounded by the bell-shape glow ; 
in fig. 23 the central bright portion and the bell-shape glow have disappeared, and 
MDCC'CLXXX. N 
