-----+--------------+--------------+----------+---------+
| | Volts. | Volts. | Volts. | Volts. |
| H2 | 1296 | 1174 | 2125 | 1550 |
| O2 | 2402 | 1975 | 2800 | 2350 |
| CO | 2634 | 2100 | .. | .. |
| CH4 | 2777 | 2317 | .. | .. |
| NO | 3188 | 2543 | .. | .. |
| CO2 | 3287 | 2655 | 3475 | 2100 |
| N2 | .. | .. | 2600 | 2000 |
| Air | .. | .. | 2750 | 2050 |
+------+--------------+--------------+----------+---------+

We see from this table that in the case of the discharge from a
positively electrified point the greater the molecular weight of the gas
the greater the potential required for discharge. Rontgen concluded from
his experiments that the discharging potential from a positive point in
different gases at the same pressure varies inversely as the mean free
path of the molecules of the gas. In the same gas, however, at different
pressures the discharging potential does not vary so quickly with the
pressure as does the mean free path. In Precht's experiments, in which
different gases were used, the variations in the discharging potential
are not so great as the variations in the mean free path of the gases.

The current of electrified air flowing from the point when the
electricity is escaping--the well-known "electrical wind"--is
accompanied by a reaction on the point which tends to drive it
backwards. This reaction has been measured by Arrhenius (_Wied. Ann._
63, p. 305), who finds that when positive electricity is escaping from a
point in air the reaction on the point for a given current varies
inversely as the pressure of the gas, and for different gases (air,
hydrogen and carbonic acid) inversely as the square root of the
molecular weight of the gas. The reaction when negative electricity is
escaping is much less. The proportion between the reactions for positive
and negative currents depends on the pressure of the gas. Thus for equal
positive and negative currents in air at a pressure of 70 cm. the
reaction for a positive point was 1.9 times that of a negative one, at
40 cm. pressure 2.6 times, at 20 cm. pressure 3.2 times, at 10.3 cm.
pressure 7 times, and at 5.1 cm. pressure 15 times the reaction for the
negative point. Investigation shows that the reac