e following is a Table of results; the gas named is that in the
vessel _a_. The smallest, greatest, and mean interval at _u_ in air is
expressed in parts of an inch, the interval _v_ being constantly 0.62 of an
inch.

Smallest. Greatest. Mean.
_
| Air, _s_ and S, pos. 0.60 0.79 0.695
|_Air, _s_ and S, neg. 0.59 0.68 0.635
_
| Oxygen, _s_ and S, pos. 0.41 0.60 0.505
|_Oxygen, _s_ and S, neg. 0.50 0.52 0.510
_
| Nitrogen, _s_ and S, pos. 0.55 0.68 0.615
|_Nitrogen, _s_ and S, neg. 0.59 0.70 0.645
_
| Hydrogen, _s_ and S, pos. 0.30 0.44 0.370
|_Hydrogen, _s_ and S, neg. 0.25 0.30 0.275
_
| Carbonic acid, _s_ and S, pos. 0.56 0.72 0.640
|_Carbonic acid, _s_ and S, neg. 0.58 0.60 0.590
_
| Olefiant gas, _s_ and S, pos. 0.64 0.86 0.750
|_Olefiant gas, _s_ and S, neg. 0.69 0.77 0.730
_
| Coal gas, _s_ and S, pos. 0.37 0.61 0.490
|_Coal gas, _s_ and S, neg. 0.47 0.58 0.525
_
| Muriatic acid gas, _s_ and S, pos. 0.89 1.32 1.105
|_Muriatic acid gas, _s_ and S, neg. 0.67 0.75 0.710

1389. The above results were all obtained at one time. On other occasions
other experiments were made, which gave generally the same results as to
order, though not as to numbers. Thus:

Hydrogen, _s_ and S, pos. 0.23 0.57 0.400
Carbonic acid, _s_ and S, pos. 0.51 1.05 0.780
Olefiant gas, _s_ and S, pos. 0.66 1.27 0.965

I did not notice the difference of the barometer on the days of
experiment[A].

[A] Similar experiments in different gases are described at 1507.
1508.--_Dec. 1838._

1390. One would have expected only two distances, one for each interval,
for which the discharge might happen either at one or the other; and that
the least alteration of either would immediately cause one to predominate
constantly over the other. But that under common circumstances is not the
case. With air in the receiver, the variation amounted to 0.2 of an inch
nearly on the smaller interval of 0.6, and with muriatic acid gas, the
variation was above 0.4 on the smaller interval of 0.9. Why is it that when
a fixed interval (the one in th