electric discharge with the chloride of silver battery. 
95 
steel rod It passes ; this, below the glass, carries a crutch M, with two ebonite pins, which 
drop into corresponding holes made to receive them in the micrometer wheel A, fig. 21 ; 
the rod has on the top, outside the jar, a cross handle h of ebonite for turning it. The 
distance of the terminals is easily regulated by means of this rod, as the micrometer 
can be read through the 'bell glass. Before admitting any gas into it, the bell glass 
was exhausted by the mercurial pump to a pressure of less than a millimetre, then filled 
with dry gas, and again exhausted and recharged. The following Tables XIV. and 
XY. show the results obtained both with spherical surfaces 1 ‘5 inch in diameter and 
3 inches radius, and also with paraboloidal point and a disc R5 inch diameter. 
Table XIV. — Striking distance between two spherical surfaces with 8040 cells. 
Eatio of striking distance. 
Eatio of electric 
viscosity. 
Gas. 
Striking distance. 
Eeferred to 
Eeferred to 
Eeferred to 
Eeferred to 
air. 
hydrogen. 
air. 
hydrogen. 
inch. 
Air 
0-082 
1-000 
0-547 
1-0000 
1-828 
Hydrogen 
0-150 
1-829 
1-000 
0-5467 
1-000 
Oxygen .... 
0-082 
1-000 
0-547 
1-0000 
1-828 
Carbonic anhydride 
0-077 
0-939 
0-513 
1-0650 
1-949 
Table XV.- 
-Striking distance between a 
point + and disc — with 8040 cells. 
Mean ratio of striking distance. 
Electric viscosity. 
Gas. 
Striking distance. 
Eeferred to 
Eeferred to 
Eatio to 
Eatio to 
air. 
hydrogen. 
air. 
hydrogen. 
inch. 
Air 
f 0-344 
L 0-300 
1-000 
0-5733 
1-000 
1-745 
Hydrogen . . . i 
r 0-600 
I 0-562 
1-808 
1-0000 
0-553 
1-000 
Nitrogen .... 
0-402 (air 0-300) 1-340 
0-7153 
0-746 
1-399 
Oxygen . . . . <j 
f 0-212 
[ 0-220 
0-674 
0-3718 
1-484 
2-689 
Carbonic anhydride \ 
r 0-120 
L 0-160 
0-441 
0-2409 
2-268 
4-149 
When charcoal terminals are used the jump of the spark is about the same as 
with other terminals having a similar shape ; the charcoal points may be separated 
when 8040 cells are used to 1’25 inch generally, and occasionally to 1'5 inch without 
breaking the arc. If the current were greater, as would be the case with larger ceils, 
the arc would no doubt be much longer. The arc presents the ordinary characters, as 
shown in fig. 22 ; but that which takes place when the terminals are vertically one 
over the other, as in our discharger, is different, on account of its being undisturbed by 
upward air currents which deflect the arc. 
The appearance of the arc is different in different gases, as will be seen in fig. 23, 
where 1 represents the arc in air ; this when examined with the microscope presents 
an evidently stratified appearance, especially in the barrel-shaped surrounding of the 
central bright spindle ; the laminae are extremely close, and seen with very great 
