Juniata sentinel and Republican. [volume] (Mifflintown, Juniata County, Pa.) 1873-1955, 1888-11-28
LIGHTNING.
Proc VIM. Thomson's Views on the
Subject of Electrical Discharges

Subject OF Electrical DiScharSes-
At recent meeting OF the British
Association Sir William Thomson, fol-
lowing Mr. Preece, discussed at length
the subject of lightning and the means
of preventing destruction by It's uis-
charges. Mr.. Thomson said he thought
that il Professor Lodge continued his
work he would find explanation OF the
very great discovery he had made In
respect to iron afIording a better dis
charge to electricity than copper. He
hoped the Professor would continue his
labors, keeping the conditions as nearly
alike as possible, and would compare,
for instance, a thin iron wire with
thin lead or brass wire OF the same
conductivIty. There was yet good
deal more to do If a proper account
were taken of inertia, and the other
point the professor Lad accentuated,
that energy must be got rid OF In some
way, either in a conductor or else
where; if in the conductor then there
must not be energy enough to melt the
conductor. An interesting fact had
been mentioned that IN row OF horses
struck by lightning only the first and
last were killed, although the discharge
passed through all, and 1t was COM
mon experiment to give n shock to a
huudred or more persons whose hands
were Joined in a circuit, and there was
no doubt that these at the ends or the
line experienced the shock more fully
than those in the middle. There were
two potent influences al work In such
cases, the want of perfect insulation
and seIf-induction. The influence of
self-Induction might be tried and the
same thing might be tried in as nearly
as possible similar insulation, the same
number of people arranged in circle.
In that case self-induction would be
more influential in causing the dis
charge TO pass through the floor be-
reath rather than keep to the compara-
lively good conductor of the ring OF
persons; or people might be ranged IN
a Zig-Zag row, and then self-induction
will not have the same tendency 10
cause the discharge TO leave the line or
the best conductors as If the bodies
were placed IN a large circle. The i'm
perfect insulation of standing on the
Ioor would be much more potent when
the persons were arranged in a wide
circle
Mr.. Presce had spoken OF the impos-
sibIlity of forming conception Oh the
enormous augmentation OF potenllal IN
the circumstances referred 10. but IL
the term ssinertia'' were usec-and the
speaker fully agreed with the judlcl-
business of that term-comparison
might be made with the steam ham,
mer OF the hydraulic ram. The begin
ing was with a comparatively gentle
force, the weight bringing down the
hammer until it produced an exceed
ingly intense action IN the blow; or
taking the hydraulic rama we'll
known analogue for high potential for
self-Induction in an electric clrcuit-it
would then lie seen that Professor
Lodges explanation was quite valid.
Referring TO what had been said about
oscillatOry discharge in ordinary light
ming, aud also as to duration OF the
charge and multiple flashes. Sir VIII
liam thought these aspects or the case
must be distinguished from one an:
other. There may be slow discharge
and Mr.. Abercromby had referred TO
ball of lightning running down the street.
AIagO had spoken OF ball OF light
ming that had entered at the window,
and had run about among people rub
bIng up against their legs like a cat.
The speaker did not attach much
credit 10 this statement, which was re-
ported by a tailor. Sir William con-
sidered that these supposed exhibitions
OF ball lightning were mostly TO be eX-
planned physiologically. People have
been looking in some direction when
the flash comes and an intense action
is produced on the centre of the retina.
Naturally, after such startling incl
dent, all eyes are moved, and each per-
son looks about to see what has hap
peRed. They look along the floor, up
wall, or toward window, and then
a spot of light, which Is the persisting
impression on the Tetina, accompanies
the movement of the eye.
The speaker believed Mr.. Preece was
right IN speaking OF the multiplicity of
flashes OF lightning, and the expert
mental evidence given by that gentle
man was entirely borne out by what
Sir William had noticed. In 1910, at
Frankfort, he had noticed triple and
gu 4druple flashes repeatedly. These
/ occurred at such short intervals of
/ time that there could be no doubt but
| that they were somehow connected,
| and yet the interval was certainly long
| enough to show that there were
several flashes. Since then he had
/ frequently seen similar phenomena.
/ Mr.. Abercromby had said it did
not seem to be a repetition of fash
| along the same course, but a succession
/ of connected flashes, and to this the
/ speaker agreed. 1t was sort OF break
/ ing down along many lines and all over
the place. Light had been spoken OF
as tending to induce flashes. 1t seemed
as if the very fine oscillations of light
actually put the air into a condition
which is more easily disruptive than ali
| which Is not agitated by light, but
that would not account for the time
interval, and Sir William thought
that something might be attribu-
ted to sound. The first flash does pro-
duce a tremendous disturbance In the
air, probably causing a very per-
feet vacuum in the place of the flash;
and after this follows a knocking to.
gether of the air. 1t was difficult tC
account for an electric flash in the all
otherwise than by supposing a crack IN
the air suddenly filling up, and that
producing an exceedingly sharp elastic
disturbance. 1t was quite possible that
that elastic disturbance, pIopagated, al
rate nearly equal to the ordinary
velocity of sound, to another place
where the air is in a state of high ten
sion, and ready to break down. would be
caused 10 break down. Thus it might
be that one flash caused considerable
I uumDcI5 OF OlucTS dL snort Intervals
1t was a most interesting subject, and
might be easily investigated further
10y the aid of photography. Many In,
teresting experiments had been mad
on the magnetiZation of steel needle:
by helix in which there are electric
oscillations. Relss found that when Z
Leyden Jar is discharged through ar
insulated wire wound up in q helix il
the ordinary way steel needles AT,
found sometimes magnetiZed in tn,
direction that would be expected from
the direction that would be expected
from the direction of the main dis
charge and sometimes in the contrar,
direction. Lord Rayleigh had men
toned differences of direction o
magnetiZation in different individ
uals of bundle of steel wires thu:
. exposed to this kind of magnetizinf