Neal our technician suddenly got
Neal our technician suddenly got

inspiration from his old physics teacher
inspiration from his old physics teacher

he's devised a machine which will allow
he's devised a machine which will allow

him to put a high current through a
him to put a high current through a

piece of thin wire and as he turns the
piece of thin wire and as he turns the

knob the current goes up and up and up
knob the current goes up and up and up

until the wire fails no I'm ready when
until the wire fails no I'm ready when

you are for this one so we started with
you are for this one so we started with

copper what happens is that as you put
copper what happens is that as you put

the current through the copper he gets
the current through the copper he gets

hotter and hotter and hotter and in this
hotter and hotter and hotter and in this

case copper melts before it catches fire
case copper melts before it catches fire

so suddenly you see the wire sagging
so suddenly you see the wire sagging

down and down and down and eventually it
down and down and down and eventually it

breaks and as it breaks there is a flash
breaks and as it breaks there is a flash

as the copper vaporizes and you may
as the copper vaporizes and you may

remember that copper gives a nice green
remember that copper gives a nice green

color in the vapor so you see a very
color in the vapor so you see a very

quick flash of green light
quick flash of green light

so Neil had a great ambition to try and
so Neil had a great ambition to try and

burn aluminium so he got piece of
burn aluminium so he got piece of

aluminium wire and heated it up but like
aluminium wire and heated it up but like

copper aluminium melts before it catches
copper aluminium melts before it catches

fire in air so suddenly you'd start
fire in air so suddenly you'd start

sagging sagging sagging and after a
sagging sagging sagging and after a

little bit its breaks Neil was a bit
little bit its breaks Neil was a bit

disappointed nothing burned
disappointed nothing burned

so we tried magnesium didn't have
so we tried magnesium didn't have

magnesium wire so we tried magnesium
magnesium wire so we tried magnesium

ribbon that's relatively flat material
ribbon that's relatively flat material

and as you heat that because the heated
and as you heat that because the heated

metal expands the magnesium started
metal expands the magnesium started

arching upwards and then suddenly it
arching upwards and then suddenly it

drooped there as probably many of you
drooped there as probably many of you

know that once you set fire to magnesium
know that once you set fire to magnesium

it keeps burning so the whole lot burnt
it keeps burning so the whole lot burnt

away with clouds of white sort of smoke
away with clouds of white sort of smoke

which essentially is finely divided
which essentially is finely divided

magnesium oxide
magnesium oxide

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magnesium is a metal that once you light
magnesium is a metal that once you light

it it generates so much heat that the
it it generates so much heat that the

burning becomes self-sustaining it's
burning becomes self-sustaining it's

probably because the metal doesn't
probably because the metal doesn't

conduct away the heat very much from the
conduct away the heat very much from the

area that's burning
area that's burning

whereas aluminium and copper if you set
whereas aluminium and copper if you set

it on fire and remove the source of heat
it on fire and remove the source of heat

it quickly goes out probably the metal
it quickly goes out probably the metal

just cools down too fast
just cools down too fast

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Neal suddenly remembered he had some
Neal suddenly remembered he had some

special wire he took Brady to his
special wire he took Brady to his

special store he calls it the dark hole
special store he calls it the dark hole

doesn't want me going there and might
doesn't want me going there and might

start taking things from it in the dark
start taking things from it in the dark

hole was the remains of a
hole was the remains of a

superconducting magnet a very powerful
superconducting magnet a very powerful

magnet that was used in an instrument
magnet that was used in an instrument

some years ago the magnet consists of a
some years ago the magnet consists of a

coil and Neil cut off a piece of this
coil and Neil cut off a piece of this

alloy the wire that's used for these
alloy the wire that's used for these

magnets has to be insulated otherwise it
magnets has to be insulated otherwise it

would short-circuit and it's insulated
would short-circuit and it's insulated

with varnish so as it heats up there's a
with varnish so as it heats up there's a

bit of smoking as the varnish vaporizes
bit of smoking as the varnish vaporizes

slightly disappointingly it behaves much
slightly disappointingly it behaves much

the same as the other metals
the same as the other metals

SAG's flashes and breaks
SAG's flashes and breaks

next Neil produced a piece of tungsten
next Neil produced a piece of tungsten

wire tungsten wire is what's used in
wire tungsten wire is what's used in

old-fashioned lightbulbs it was really
old-fashioned lightbulbs it was really

interesting as you heat it up it gets
interesting as you heat it up it gets

hotter and hotter tungsten has the
hotter and hotter tungsten has the

highest melting point of any of the
highest melting point of any of the

metals that we used and it starts to
metals that we used and it starts to

burn doesn't melt at all and just gets
burn doesn't melt at all and just gets

thinner and thinner and thinner until it
thinner and thinner and thinner until it

fails he ended up with quite a
fails he ended up with quite a

terrifying looking spike a really narrow
terrifying looking spike a really narrow

tungsten so professor this did fail
tungsten so professor this did fail

quite quickly but light bulbs don't fail
quite quickly but light bulbs don't fail

quickly ideally what's the difference
quickly ideally what's the difference

between this and a light bulb the
between this and a light bulb the

difference from the light bulb is that
difference from the light bulb is that

in a light bulb the tungsten is not as
in a light bulb the tungsten is not as

hot as at the end of Neil's experiment
hot as at the end of Neil's experiment

and of course the bulb itself is filled
and of course the bulb itself is filled

with argon gas rather than with air Neil
with argon gas rather than with air Neil

and I were both really quite fascinated
and I were both really quite fascinated

by this very narrow spike that is made
by this very narrow spike that is made

and I think it is because one part of
and I think it is because one part of

the wire must have started getting
the wire must have started getting

thinner than the rest and therefore
thinner than the rest and therefore

hotter and therefore preferentially the
hotter and therefore preferentially the

hottest part will have burnt fastest
hottest part will have burnt fastest

Brady really wanted to do gold Neil was
Brady really wanted to do gold Neil was

a bit reticent gold is expensive so he
a bit reticent gold is expensive so he

put a glass dish underneath now I must
put a glass dish underneath now I must

say that gold was probably the most
say that gold was probably the most

disappointing of them all because it
disappointing of them all because it

heated up it melted it broke
heated up it melted it broke

it didn't give a really very convincing
it didn't give a really very convincing

flash Gold doesn't have a beautiful
flash Gold doesn't have a beautiful

green color like copper but Brady was
green color like copper but Brady was

satisfied
satisfied

Anil didn't lose any gold I think the
Anil didn't lose any gold I think the

most exciting metal and this was a real
most exciting metal and this was a real

surprise was molybdenum when we heated
surprise was molybdenum when we heated

up molybdenum even when I was watching
up molybdenum even when I was watching

the camera from the distance there
the camera from the distance there

seemed to be some sort of pulsating on
seemed to be some sort of pulsating on

the picture
the picture

and when we looked at the metal
and when we looked at the metal

afterwards it was extraordinary
afterwards it was extraordinary

because instead of having a smooth wire
because instead of having a smooth wire

there were little blobs of molybdenum
there were little blobs of molybdenum

metal all the way along the wire and
metal all the way along the wire and

these blobs were really quite evenly
these blobs were really quite evenly

spaced
spaced

now it turns out that this phenomenon
now it turns out that this phenomenon

has been seen in exploding wires using
has been seen in exploding wires using

very high speed cameras
very high speed cameras

I think it's unusual i and none of my
I think it's unusual i and none of my

colleagues had seen like anything like
colleagues had seen like anything like

this before
this before

now you probably or some of you who
now you probably or some of you who

specialist in this area probably have
specialist in this area probably have

some really good explanation of why this
some really good explanation of why this

happened I think what happened is that
happened I think what happened is that

the molybdenum ëtil began to melt on the
the molybdenum ëtil began to melt on the

surface of the wire so you imagine the
surface of the wire so you imagine the

wire covered with a thin layer of liquid
wire covered with a thin layer of liquid

and because liquid has surface tension
and because liquid has surface tension

this is why liquid forms drops I think
this is why liquid forms drops I think

that the liquid separated into little
that the liquid separated into little

drops because the surface tension pulled
drops because the surface tension pulled

it together and so you get what would
it together and so you get what would

normally be little drops of liquid but
normally be little drops of liquid but

they solidified so we've somehow got
they solidified so we've somehow got

them fossilized along this wire all my
them fossilized along this wire all my

colleagues that I've shown these bits of
colleagues that I've shown these bits of

wire to have got really excited it's
wire to have got really excited it's

really surprising that you can get such
really surprising that you can get such

an even spacing I did a bit of research
an even spacing I did a bit of research

on this phenomenon and I came across a
on this phenomenon and I came across a

word I'd never heard before called
word I'd never heard before called

angeloids angeloids
angeloids angeloids

is the word that mathematicians use to
is the word that mathematicians use to

describe this sort of object I would be
describe this sort of object I would be

very interested to hear from any of you
very interested to hear from any of you

who has a really good explanation of
who has a really good explanation of

what happened Neil thinks that the
what happened Neil thinks that the

spacing might be related to the
spacing might be related to the

frequency of the mains so he's keen to
frequency of the mains so he's keen to

try and use direct current rather than
try and use direct current rather than

alternating current and see whether we
alternating current and see whether we

get the same effect I think there'll be
get the same effect I think there'll be

no difference I had the idea that we
no difference I had the idea that we

should turn the apparatus through 90
should turn the apparatus through 90

degrees so the wire is vertical and it
degrees so the wire is vertical and it

would be much more difficult for it to
would be much more difficult for it to

sag and what we found was indeed it
sag and what we found was indeed it

didn't sag so much at least until it
didn't sag so much at least until it

break and we got a much better shot of
break and we got a much better shot of

the flesh of
the flesh of

green light as the cup of vaporized
green light as the cup of vaporized

there was still slight bending but it
there was still slight bending but it

was much less than before just as we
was much less than before just as we

were packing up I persuaded Neel to make
were packing up I persuaded Neel to make

a coil of copper we put this coil
a coil of copper we put this coil

vertically my idea was that the coil
vertically my idea was that the coil

would be floppier than the straight
would be floppier than the straight

piece of wire so it might sink more
piece of wire so it might sink more

but then it collapsed quite
but then it collapsed quite

spectacularly once it's broken
spectacularly once it's broken

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but I think chemically what was
but I think chemically what was

interesting to me was that if you looked
interesting to me was that if you looked

at the bit that was broken you could see
at the bit that was broken you could see

the black copper to oxide on the surface
the black copper to oxide on the surface

of the copper showing that there was at
of the copper showing that there was at

least some reaction with oxygen but very
least some reaction with oxygen but very

much less than saying the burning
much less than saying the burning

magnesium I was really grateful to Neil
magnesium I was really grateful to Neil

because he devised a demonstration which
because he devised a demonstration which

almost turned into an experiment which
almost turned into an experiment which

made me think I never thought that piece
made me think I never thought that piece

of molybdenum wire could be in the least
of molybdenum wire could be in the least

bit interesting and Here I am
bit interesting and Here I am

the day after Neil did the experiment
the day after Neil did the experiment

still thinking about it and anything
still thinking about it and anything

that makes scientists think is really
that makes scientists think is really

good and anything that makes us think
good and anything that makes us think

differently is brilliant
differently is brilliant

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you
you

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you
you