g the electrolyte. It is
even possible, that with different electrolytes or dielectrics the ratio
may be considerably varied, or in some cases even inverted.

[A] Philosophical Transactions, 1838, p. 47.

* * * * *

_Glow discharge._

1526. That form of disruptive discharge which appears as a _glow_ (1359.
1405.), is very peculiar and beautiful: it seems to depend on a quick and
almost continuous charging of the air close to, and in contact with, the
conductor.

1527. _Diminution of the charging surface_ will produce it. Thus, when a
rod 0.3 of an inch in diameter, with a rounded termination, was rendered
positive in free air, it gave fine brushes from the extremity, but
occasionally these disappeared, and a quiet phosphorescent continuous glow
took their place, covering the whole of the end of the wire, and extending
a very small distance from the metal into the air. With a rod 0.2 of an
inch in diameter the glow was more readily produced. With still smaller
rods, and also with blunt conical points, it occurred still more readily;
and with a fine point I could not obtain the brush in free air, but only
this glow. The positive glow and the positive star are, in fact, the same.

1528. _Increase of power in the machine_ tends to produce the glow; for
rounded terminations which will give only brushes when the machine is in
weak action, will readily give the glow when it is in good order.

1529. _Rarefaction of the air_ wonderfully favours the glow phenomena. A
brass ball, two and a half inches in diameter, being made positively
inductric in an air-pump receiver, became covered with glow over an area of
two inches in diameter, when the pressure was reduced to 4.4 inches of
mercury. By a little adjustment the ball could be covered all over with
this light. Using a brass ball 1.25 inches in diameter, and making it
inducteously positive by an inductric negative point, the phenomena, at
high degrees of rarefaction, were exceedingly beautiful. The glow came over
the positive ball, and gradually increased in brightness, until it was at
last very luminous; and it also stood up like a low flame, half an inch or
more in height. On touching the sides of the glass jar this lambent flame
was affected, assumed a ring form, like a crown on the top of the ball,
appeared flexible, and revolved with a comparatively slow motion, i.e.
about four or five times in a second. This ring-shape and revolution a