insulating pillars,
_h_ and _i_, to which were fixed two brass balls, and through these passed
two sliding rods, _k_ and _m_, terminated at each end by brass balls; _n_
is the end of an insulated conductor, which could be rendered either
positive or negative from an electrical machine; _o_ and _p_ are wires
connecting it with the two parts previously described, and _q_ is a wire
which, connecting the two opposite sides of the collateral arrangements,
also communicates with a good discharging train _r_ (292.).

1385. It is evident that the discharge from the machine electricity may
pass either between _s_ and _l_, or S and L. The regulation adopted in the
first experiments was to keep _s_ and _l_ with their distance _unchanged_,
but to introduce first one gas and then another into the vessel _a_, and
then balance the discharge at the one place against that at the other; for
by making the interval at _a_ sufficiently small, all the discharge would
pass there, or making it sufficiently large it would all occur at the
interval _v_ in the receiver. On principle it seemed evident, that in this
way the varying interval _u_ might be taken as a measure, or rather
indication of the resistance to discharge through the gas at the constant
interval _v_. The following are the constant dimensions.

Ball _s_ 0.93 of an inch.
Ball S 0.96 of an inch.
Ball _l_ 2.02 of an inch.
Ball L 0.62 of an inch.
Interval _v_ 0.62 of an inch.

1386. On proceeding to experiment it was found that when air or any gas was
in the receiver _a_, the interval _u_ was not a fixed one; it might be
altered through a certain range of distance, and yet sparks pass either
there or at _v_ in the receiver. The extremes were therefore noted, i.e.
the greatest distance short of that at which the discharge _always_ took
place at _v_ in the gas, and the least distance short of that at which it
_always_ took place at _u_ in the air. Thus, with air in the receiver, the
extremes at _u_ were 0.56 and 0.79 of an inch, the range of 0.23 between
these distances including intervals at which sparks passed occasionally
either at one place or the other.

1387. The small balls _s_ and S could be rendered either positive or
negative from the machine, and as gases were expected and were found to
differ from each other in relation to this change (1399.), the results
obtained under these differences of charge were also noted.

1388. Th