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 are beautifully connected with the mechanical currents (1576.) taking place within the receiver.  These glows in rarefied air are often highly exalted in beauty by a spark discharge at the conductor (1551. Note.).

1530.  To obtain a negative glow in air at common pressures is difficult.  I did not procure it on the rod 0.3 of an inch in diameter by my machine, nor on much smaller rods; and it is questionable as yet, whether, even on fine points, what is called the negative star is a very reduced and minute, but still intermitting brush, or a glow similar to that obtained on a positive point.

1531.  In rarefied air the negative glow can easily be obtained.  If the rounded ends of two metal rods, about O.2 of an inch in diameter, are introduced into a globe or jar (the air within being rarefied), and being opposite to each other, are about four inches apart, the glow can be obtained on both rods, covering not only the ends, but an inch or two of the part behind.  On using balls in the air-pump jar, and adjusting the distance and exhaustion, the negative ball could be covered with glow, whether it were the inductric or the inducteous surface.

1532.  When rods are used it is necessary to be aware that, if placed concentrically in the jar or globe, the light on one rod is often reflected by the sides of the vessel on to the other rod, and makes it apparently luminous, when really it is not so.  This effect may be detected by shifting the eye at the time of observation, or avoided by using blackened rods.

1533.  It is curious to observe the relation of glow, brush, and spark to each other, as produced by positive or negative surfaces; thus, beginning with spark discharge, it passes into brush much sooner when the surface at which the discharge commences (1484.) is negative, than it does when positive; but proceeding onwards in the order of change, we find that the positive brush passes into glow long before the negative brush does.  So that, though each presents the three conditions in the same general order, the series are not precisely the same.  It is probable, that, when these points are minutely examined, as they must be shortly, we shall find that each different gas or dielectric presents its own peculiar results, dependent upon the mode in which its particles assume polar electric condition.

1534.  The glow occurs in all gases in which I have looked for it.  These are air, nitrogen, oxygen, hydrogen, coal gas, carbonic acid, muriatic acid, sulphurous acid and ammonia.  I thought also that I obtained it in oil of turpentine, but if so it was very dull and small.

1535.  The glow is always accompanied by a wind proceeding either directly out from the glowing part, or directly towards it; the former being the most general case.  This takes place even when the glow occurs upon a ball of considerable size:  and if matters be so arranged that the ready and regular access of air to a part exhibiting the glow be interfered with or prevented, the glow then disappears.