238 
NATURE 
[ Zan. 19, 1871 

across the tube. The positive pole alone was observed to be 
luminous when the current was very minute, and the negative 
only was luminous when the current was strong. 
experiments were tried, and the results, which have been photo- 
graphed, accompany the paper. A current was passed through the 
tube U and the vacuum ; the U tube contained pure glycerine, 
and had a very large resistance, which was gradually reduced. 
At the commencement it was more than 10,000 megohms ; the 
upper or small ring was positive, the lower ring was negative. 
The power was so reduced that the faintest possible light only 
was visible ; in this case the positive wire alone was luminous, 
whether it were the large or small ring that was positive. The 
light was so feeble that, though the experiment was conducted 
in a perfectly dark room, we were sometimes unaware whether 
the current was passing or not. An exposure of thirty minutes’ 
duration left, as will be seen, a very good photographic record 
of what was taking place; this means of viewing light too 
feeble for the eye may receive other applications. The resistance 
was then reduced, when the light became much more brilliant, — 
a tongue of light projected from the positive pole towards 
the negative, the latter being still almost completely obscure. 
The light around the positive pole was to all of our eyes white, 
while the projecting flame was a bright brick-red. This bright 
brick-red, however, possessed great photographic power. ‘The 
negative wire at this stage began to show signs of luminosity. 
As the power was increased, the flame became detached from 
the positive pole. On still further increasing the power, the 
positive pole ceased to be luminous; and on still further 
increasing the power, by removing the U tube altogether, the light 
surrounded the negative wire, the photograph shows a white 
flattened hour-glass, apparently detached from the wire ; to the 
eye, however, the wire appeared to be surrounded by a bright 
blue envelope } inch in diameter, which did not possess suffi- 
cient photographic power to leave a record of itself, while the 
red portion did so. A large condenser was now attached to the 
battery, and discharged through the tube (the condenser had a 
capacity of 27 microfarads) ; this was equivalent toa momentary 
contact with a battery of little or no resistance. The flash was 
exceedingly brilliant to the eye ; it could be heard outside the 
tube with a sharp click ; the eye, however, was so dazzled as not 
to be able to see its shape. The light was confined entirely to 
the ositive pole; thus, then, as the power is increased from 
nothing upwards, the first pole to become luminous is the 
positive ; secondly, the two poles become luminous ; thirdly, the 
negative pole alone is luminous; and fourthly, with an instan- 
taneous discharge, the positive pole only is luminous. When 
the resistance in the U tube was greatly reduced, and a galvano- 
meter (not very sensitive) was inserted, so that the chief 
resistance in circuit was that of the exhausted tube, as the 
potential was augmented cell by cell, the changes took place 
abruptly and suddenly. For example, when the power was so 
low that the positive pole only was visible, the current was feeble, 
and kept augmenting in power as cell after cell was added on. 
Suddenly the luminous red flame made its appearance, and the 
galyanometer showed that the current had suddenly augmented 
three or four times in power. As the power was again further 
increased, cell by cell, the current again steadily augmented in 
proportion, until the luminous tongue suddenly disappeared, the 
galvanometer showing a still further sudden increase in the 
current, 
Nature of the luminous cloud.—Piiicker has shown that when 
such an exhausted tube, with a current through it, is placed 
between the poles of an electro-magnet, a luminous arch is pro- 
duced, which arch follows the course of the magnetic rays. As 
the electro-magnet is magnetized, the tube, which before was full 
of a luminous cloud, is seen gradually to change ; the magnet 
gathers up this diffused cloud, and builds up an arch. Inasmuch 
as the electricity was passing in a continuous current from the 
battery, from wire to wire, it is evident the light is projected 
right and left into those parts of the tube where there is no 
electric current flowing. To endeavour to ascertain the nature 
of this arch, a tube was constructed. A piece of talc, bent into 
the form U, had a fibre of silk stretched across it ; on this fibre 
of silk was cemented a thin strip of talc, 1 inch in length, ¥5 inch 
broad, weighing about +4; of a grain, The tube was sealed up 
and exhausted ; carbonic acid and potash were used to get a high 
vacuum. When the magnet was not magnetized, the passage of 
the current from wire to wire did not affect the piece of tale. 
When the magnet was charged, and the luminous arch was made 
to play upon the lower portion of the talc, it repelled it, no 
The following | 

matter which way the electric current was passing. When the 
tube was shifted over the poles of the magnet so as to project the 
luminous arch against the upper part of the tale, the upper end 
of the talc was repelled in all instances ; the arch, when pro- 
jected against the lower part of the talc, being near the magnet, 
was more concentrated, and the angle of deviation of the tale was 
as much as 20°.. When the upper part of the arch, which was 
much more diffused, was thrown upon the upper part of the tale, 
it was repelled about 5°. This experiment, I think, indicates 
that this arch is composed of attenuated particles of matter pro- 
jected {rom the negative pole by electricity in all directions, but 
that the magnet controls their course, and these particles seem to 
be thrown by momentum on each side of the negative pole, 
beyond the limit of the electric current. This arch requires time 
for its formation, for when a charged condenser is discharged 
through the tube no arch is produced. The arch from the nega- 
tive pole is a hollow cylinder; the little tale tell-tale against 
which the arch was projected cut out the light, and a correspond- 
ing dark space existed throughout the remainder of the course of 
the arch. There was on the talc, at the spot where the arch 
struck it, a little bright luminous cloud, as though the attenuated 
luminous vapour was condensed by this material obstruction. 
Great care had been taken not to let the arch strike the single fila- 
ment of silk which suspended the tale. Having demonstrated that 
the talc was repelled as described, the arch was allowed to play 
against the silk fibre, which the author expected would have been 
instantly burnt ; such, however, was not the case. Even whena 
powerful induction-coil replaced the battery, the fibre remained 
unhurt. 
Comparison of the above phenomena with discharges between the 
poles of a Holt?s Machine im air.—In the first part of this paper 
four different kinds of discharges were described zz vacuo, With 
a ‘* Holtz’s” machine, which will give 11-inch sparks in the air, 
four well-marked different kinds of discharge have been obtained 
in the air; one of which, the author thinks, will explain the 
curious and rare phenomenon known as “‘ ball lightning.” In 
the experiments hereafter referred to, the condensers were in all 
cases attached to the ‘‘ Holtz’s “ machine. The first discharge is 
the long 11-inch zigzag spark or lightning-flash ; the second is 
the well-known ‘‘ brush,” which is best obtained by connecting 
the negative pole of the ‘‘ Holtz’s” machine to the earth; the 
third kind of discharge isa hissing red flame, } inch in length, 
playing about the negative pole, the positive pole being scarcely 
luminous at all, and if luminous, at one or two points only ; the 
fourth or most remarkable phenomenon is best obtained in the 
following manner (I should here remark that the brass balls on 
each of the poles are about an inch in diameter) :—Tie to the 
negative pole a small thin strip or filament of wood three inches 
in length, and bent so as to’project on each side of the negative 
pole, and a little beyond it towards the positive. On rotating the 
machine, two bright spots are seen upon the positive pole. It the 
positive pole be made to rotate upon its axis, the luminous spots do 
not rotate with it; if, however, the zegative ole, withits filament of 
wood, be rotated, the spots on the Jositive pole obey it, and rotate © 
also. The insertion of a non-conductor, such as a strip of glass, 
in front of the projecting wooden end, obliterates the luminous 
spot on the positive pole. When the author first discovered this, 
he, seeing apparently pieces of dirt on the positive pole, wiped 
it clean with a silk handkerchief, but there they remained in spite 
ofall wiping ; he then examined the negative pole, and discovered 
a minute speck of dirt corresponding to the luminous spots on the. 
positive pole. When the filament of woodis removed from the nega- 
tive pole there issometimesa luminosity or glow over a large portion 
of the surface of the positive ball, Ifin this state three or four little 
pieces of wax, or even a drop or two of water, be placed upon the 
negative pole, corresponding non-luminous spots will be found 
upon the positive pole, which rotate with the former, but do not 
with the latter. It is therefore evident that there are lines of 
force existing between the two poles, and by these means one is 
able to telegraph vo the negative ¢o the positive pole to a dis- 
tance of 8 inches through the air, without any other conductor 
than that which the electrical machine has constructed for itself 
across the non-conducting gas. The foregoing seems to the 
author to give a possible explanation of “ ball-lightning ;” if it 
be possible for there to be a negatively electrified cloud suffi- 
ciently charged to produce a flash from the earth to the cloud, a 
point in the cloud would correspond to the wood projection on 
the negative conductor; if such a cloud exist, a luminous spot 
would be seen moving about the surface of the earth, correspond-~ 
ing to the moying point of cloud over it, and thus present 
