Irving Langmuir's Ball Lightning Tube

This article from Wayne Strattman at MIT. The source is unknown, perhaps it's from Scientific American from the 1920's or 30's. The photos are unrecognizable, having gone through many generations of photocopying. I know of no modern attempts to replicate this device. - Bill Beaty 10/95
[Update: Steve L thinks it's from the Gernsback magazine "The Experimenter" of Feb. 1925]
[Update: very probably this video shows the BL-tube in action: G.E. film 1941: TAKING THE X OUT OF X-RAYS, see 0:12 to 0:18]


The history of modern physics is replete with experiments on gaseous conduction. The field seems especially rich in possibilities, chiefly perhaps because we are there concerned more directly with that fundamental factor in electrical phenomena- the electron. Gasses under atmospheric conditions have comparatively low densities; that is; their molecules are placed further apart than in solids or liquids, and the electrons have larger spaces over which to roam aimlessly or to fly rapidly, impelled by electromagnetic forces. In rarefied gases, the motions of the electrons are far more vigorous than in everyday conditions.

Free for a moment from the influence of the atom, the electron will display unusual properties and give rise to phenomena whose beauty and novelty contribute much to the prevalent interests in electrical conduction through low pressure gases.

Observe, for instance, the photograph in Fig. 1. That tenuous electrical discharge, so beautifully simple, is coupled with myriads of agile particles that move about, impatiently swaying now under the influence of electric, now under magnetic forces. This is no ordinary discharge through a vacuum, but one actuated by some, as yet unknown, forces. A moment before the picture was taken, the arc was stretched motionless through the tube, glowing with a quiet purplish red color. Then through a momentary interruption of current, the arc gains life and tears itself away from the tube with the writhing motion of a snake, while from a tungsten filament at the base of the tube melted tungsten is sputtered and (Continued on page 255)

bright blue flashes are sent up the vertical stem.

This spectacular and beautiful electrical discharge which gives promise of leading to a grater understanding of vacuum phenomena was produced in the research laboatories of the General Electric Company, by Dr. Irving Langmuir, C.G. Found, and A.F. Dittner, prominent Americal physicists.

And yet at first glance the apparatus in which these curious phenomena take place seems to differ only in shape from the ordinary two-electrode vacuum tube, and essentially is similar to the argon-filled tungar rectifying bulb. Fig. 2 shows a sectional view of it. The large glass cylinder is 15cm (5.9 inches) long and 10cm (3.9 inches) diameter, and contains a single loop tungsten filament at each end. To this cylinder is welded a slender glass tube 50 cm. (20 inches) long and 3 cm (1.2 inches) in diameter at the upper end of which a disc electrode is mounted.

Now the filament is supplied with current at a low potential and is brought to incandescence at a very high temperature, about 2500C (4532F) Then 250 volts are applied between the plate and the filament, but as yet no glow appears in the tube. The ionization in the tube is insufficient, but can be much increased by approaching a terminal of a high frequency coil to the glass tube. This done, an electric arc of the characteristic argon color appears in the tube. The arc draws one ampere and the potential from the plate to filament drops to 25 volts.

Nothing unusual is involved in this action, but let the filament circuit be opened for only one-half second and a sequence of most remarkable electrical phenomena ensues. The momentary decrease in filament temperature causes a rise in the voltage across the arc by reducing for an instant the electronic emission from the filament. The voltage rising to about 100, causes a sputtering of the filament and small quantities of tungsten are shot into the arc. Though the tungsten so emitted is only about .000001 grams, its effects are astonishing. The arc which before the "sputtering of tungsten" filled the tube and was insensible to the influence of a magnetic field, now detaches itself from the walls and can be attracted or repelled by a permanent magnet held near the tube.

The arc now has an altered appearance. It has a central reddish core, which bears a positive charge and is about 1cm in diameter. In this red column positively charged argon atoms are moving and vibrating under the influence of the electric field between the plate and the filament. Immediately surrounding this region is a thin dark space, and beyon this a bright yellow sheath of glowing gas. This sheath is negatively charged and gradually disappears, the central part of the arc increasing in size until it almost fills the tube. In place of the yellow "skin," a thin layer of negative charges remains. This, together with a positive layer around the reddish arc, forms what is called an "electric double-layer"; that is, two invisible sheaths extremely close to each other, the inner one bearing a positive while the outer a negative space charge.

If an ordinary horseshoe magnet is brought near the tube, the arc is deflected, as is any conductor carrying a similar current. At the same time the yellow skin appears on the opposite side of the arc on the side not in contact with the wall.

As the magnet is brought nearer, the yellow skin becomes brighter and thinner, and curiously begins to act like a liquid. Slowly, tiny drops of golden yellow liquid fire are formed. They move along the surface, only to break away and fall, molten spheres of bright white light into the arc. By regulating the intensity of the magnetic field, these droplets or globules, ranging from a few tenths mm up to 5 or 6 mm in diameter (about the size of a pea) can be made to form slowly and detach themselves singly from the skin of the arc. By proper combination and longitudinal and transverse fields the globules may often be made to move upwards or downwards in the arc parallel to its axis for distances ou to 5 or 10 cm, 2 to 4 inches. Under certain conditions the globules have been observed to move very slowly so that their motions through the arc could be easily followed by the unaided eye. But more often they move with the velocity of about a foot per second, and thus appear as brilliant lines or filamentary streamers. See Fig. 3 where several streamers with nearly parallel paths are shown.

These streamers are formed by the influence of the magnetic field, and vary in appearance with the magnitude of the current flowing through the arc. If this current is varied, the motion of the streamers will be correspondingly affected. Thus, by superimposing an alternating current on the direct current fed to the anode, that is, the disc electrode, the streamers of individual globules will move in a sinusoidal path. That is, they will appear as a sine wave which is characteristic of alternating currents. The streamers will reproduce accurately the wave shape of the current even (Continued on page 284)

at frequencies up to 1000 cycles. A similar effect is produced by using alternating current for heating the filament. In either case the globule streamer assumes a wave motion, travelling across the arc in beautifully sharp curves, rather than in straight lines.

If the arc current is maintained, this effect continues for hours before the minute portion of tungsten ceases to act. The effect can then be brought back by again cutting out the filament current for a moment and thus sputtering another trace of tungsten into the argon vapor. If the arc current is shut off for about 40 seconds, the effect disappears- the tungsten has been deposited and the streamer discharge will not start again until more of the metal has been sputtered from the filament.

According to this theory, tungsten atoms, negatively charged, roam about in the spaces outside the arc. These atoms entering the "electric double layer" lose their charge and collect on the positive sheath, forming small globules. At these points on the double layer the negative sheath is indented, and when sufficient tungsten accumulates, this indentation becomes sharp and will extend into the arc until the globules tear away. By the nature of their formation the globules will thus have a positive sheath on the outside and a negative sheath on the inside; and arrangement the reverse of that found in the arc proper.

These glowing detached globules seem to have characteristics similar in many respects to those that have been described as belonging to ball lightning. It is perhaps not certain that ball lightning is anything more than a psychological phenomenon, but if it has objective reality, it may possibly be due to causes similar to those which give rise to the globules described above. The ions of a highly ionized gas, such as the electrified atmosphere, recombine on solid particles forming small spheres, the solid particles being retained within the ball by their charges and the electric field being retained at the surface of the ball. This theory is very effectively supported by the marked resemblance between ball lightning and the globules of liquid fire produced in Dr. Langmuir's experiments.

Fig. 1
Mr. Found of the General Electric Experimenting with the streamer discharge, has the miniature ball lightning formed in the tube under perfect control. Under the influence of the horseshoe magnet, these balls of fire can be made to move up and down the tube.


Fig. 2
Above: A cross-sectional view of the discharge tube in which the phenomenon of ball lightning was observed. The tube is filled with argon at very low pressure, and with the filament heated to incandescence, a reddish arc is formed between the plate and the terminal.

Fig. 3
Left: The agitation in the argon arc which is writhing like some strange electric snake, is caused by a sputtering of melted tungsten from the incandescent filament at the base of the tube.

Fig. 4
The argon arc shown at left is deflected with a magnet. The transverse, filamentary streamers are in reality small globules of incandescent tungsten moving rapidly across the arc. The globules of liquid fire are, in formation and behavior, very similar to the incandescent spheres of ball lightning. These unusual effects are produced by only .000001 gram of tungsten emitted by the filament.

Fig. 5-1
Fig. 5-2
Fig. 5-3
Fig. 5-4

In a tube filled with argon gas small globules of liquid fire have been formed, which bear a strong resemblance to ball lightning. A magnet draws the argon arc to one side of the tube and negatively charged tungsten atoms emitted by a filament move into the arc (Fig. 5-1) Near the edge of the arc they cross a region called the electric double layer bearing opposite charges on the two sides. Here the atoms lose their charge and collect in groups (Fig. 5-2) The neutral tungsten atoms thus form small masses of liquid tungsten on the border of the arc, and the layer of negative charges bends into the arc (Fig. 5-3.) This indentation continues until becoming very sharp the tungsten globule becomes detached and forms a rapidly moving miniature ball lightning (Fig. 5-4.)
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