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this talk is to be the first of a series

of three on magnetism and I'll introduce

the series by saying something about

magnetism in general it's a very

familiar effect we' probably all played

with magnets it's been known a very long

time Greeks knew about the load stone

stone that found in the earth and which

has the property of attracting iron the

Chinese were familiar with it the

Chinese also knew also knew of another

effect the load Stone was known because

it picked up small pieces of iron but

the Chinese knew also that if you

floated a load Stone so it could turn

freely they generally floated it on a

little sorcer in water it always pointed

North and South we say the compass

Points North the Chinese being Chinese I

suppose say that it points South

actually of course it Points North and

South some of you may remember that in

that very good story Puck of puk's hill

by Roger Kipling there was a yellow man

who went voyaging with the heroes uh and

had this magic load Stone which pointed

North and

South though it's so familiar however

manism is very hard to

grasp it's a magical kind of

effect doesn't correspond to anything we

are familiar

with that's my first point my second

point is

this I'm not going to explain

magnetism science can only explain

things that happen phenomena as they're

called in science in terms of something

simpler menm and electricity are two of

the things which are so simple that we

just have to take them for granted

perhaps someday we'll get a deeper

understanding of how they arise but at

present we explain things in terms of

them and what I shall say about

magnets is that magnets are magnets

because they're made up of little

magnets and we have to leave it at

that well I'll start off with something

familiar well perhaps not so familiar

because though most of you have heard of

a load Stone some of you may not have

seen one I've got a load Stone here and

this loadstone has the property of

attracting small pieces of iron iron

filings that I've got in Dish here if I

just take it and dip it in the

dish you will see it picks up quite a

respectable Little Beard of iron filings

showing that it attracts these pieces of

iron we're more familiar with magnets

made of steel when I was young the best

kind of magnet made of steel was just

made of ordinary hard steel one like

I've got here this is one of the old

familiar horseshoe

magnets now this magnet is not really

very strong I might describe it perhaps

by saying it's a few pin power because

if I dip it in this little pot of pins

you see it can pick up a fairly

respectable number of pins the ones I

played with a boy were even Feer than

this now it's one of the romanes

of those who deal in this field that

magnets have been made so very much

better generally industry is content if

it improves a thing two or three times

for instance steel we'd be very pleased

indeed if we doubled the strength of

steel by making some new

composition but in the case of

magnets Research into the way they work

has led to a quite extra Improvement in

their strength measuring their strength

by a convenient index one can say that

modern magnets are about a 100 times as

good as this one I've got one of these

modern magnets here for

instance you saw what that little one

would do with the pins now see what I

can do with this one and some

Nails you see I pick every single nail

out of the box I've got a sheet of pp

between the men and the nails because

otherwise it's so hard to coax them all

back in their box again but this makes

it quite

easy then again the compass pointing

North why does it Point North that's

because the Earth is a large magnet we

don't understand properly yet why but it

behaves as if it were one large magnet

and the compass points north north and

south because it's attracted by the

poles of the Earth here is our

Compass I placed this compass on this

pin

here and then it rotate and you will see

it always tries to Point North and

South if I displace it from its position

the red end will try and Point again

towards the North Pole there it comes

back and now you see there it is

pointing towards the North Pole

pole that is not the original

Compass the original Compass was a load

Stone the thing that chinan used in P

Poots hill was a load Stone and let's

make one of the old primitive compasses

here's my load Stone I'll float it on

this cork in

water and you will see It'll try to turn

around now so that it points towards the

north of course a wonderful Discovery in

the old days when they were able to

navigate with the help of a

compass now here's another familiar

effect um with magnets they behave as if

they had different

ends one end we call the North End of

the magnet the other end the south end

of the magnet the names are got because

it's the North End of the magnet that

tries to point towards the North Pole of

the

earth like poles repel each other unlike

poles attract each

other a simple way first again here I

painted these so they North Poles are

both red and their South poles are blue

if I approach red to Red you see it

pushes it

away here I put it in the other side and

back it comes

again where

the like pose two Blues repelling each

other

unlike poles I put the red near the blue

and you see it pulls it strongly towards

it here it is following it right round

and

round so that like ends of a magnet

repel each other unlike ends

attract in this type of magnet the

effects not very strong but again I've

got here two of these very beefy

magnets they're being held together now

they're attracting each other like that

I can pull them apart

now if I turn them

round so that like poles are

together like

that however hard I try I can't make

those two go together

watch it's absolutely impossible because

when they do it like that it's the

unlike ones attracting I feel as if

they're repelling each other most

violently here's another way of showing

this

strong attraction and repulsion I don't

know how many of you have read guler's

travels Swift's famous book but you

remember one of the countries he went to

called leuta it was governed from an

island that floated in the air and when

he was taken up there and shown into the

secret he was told uh that underneath

their Island was a very strong magnet

there that strong magnet that kept it

floating in the air of course it was

just a fairy story of Swifts and rather

a joke on the scientists at that time

but I'll show you an actual magnet

floating in the air as if nothing was

with nothing holding it up this magnetic

material is rather like the load Stone

it's not iron it's a kind of oxide of

iron and I've got some rings made of it

so their South Poles were the bottom and

their North Poles are on top of the Ring

now we put a pile of them there we'll

end up with a South Pole in the top here

and put a South Pole opposite it and you

will see the repulsion is so strong that

that will float right up in the

air so we could build a little city on

top of that and there it would be

floating with nothing to hold it up now

I'll show you an experiment to

illustrate another property of these

magnetic materials and that is that if

you've got a

magnet and put a piece of iron near it

it turns that piece of iron into a

magnet although the iron is not a magnet

to begin with

itself as we say it induces magnetism in

the arm here are a series of cylinders

they're not magnetized at all they're

quite inert I put them together like

that they have no attraction for each

other but if I take my powerful magnet

here

and stick that piece of iron onto it

that passes on its magnetism as it were

through this AR so it'll now be magnetic

there as you can see I can put another

cender onto it and we can go on here's

another one I'm the magnetic property is

passing right along still another and if

I have a steady hand perhaps I could put

just this end well on here it's holding

up whole lot by passing on its magnetism

by inducing it in that way

now we're very proud at the Royal

Institution one of our great people who

worked here for over 40 years was

Michael Faraday one of the greatest

scientists of all time and Faraday

thought a lot about these forces of

nature and one idea which he established

is that we ought to think of this these

magnets in rather a different way to the

way in which I've talked about them so

far

I've talked about they're having North

and South

poles as if there was something at the

end of the magnet which was a pole and a

South Pole repels another South Pole and

attracts a North Pole far looked at it

in a different way it was an important

way he said we must think that when

there's a magnet present in some place

it has done something to all the space

around it it's created what he called a

field a magnetic field it's alter the

properties of this space and around each

of these magnets there is one of these

magnetic fields and another magnet

Fields this field as it were and behaves

accordingly we've so seen for instance

that a magnet makes a neighboring piece

of iron a magnet what we'll say now is

put a piece of iron in a magnetic field

and it becomes a

magnet parad then pictured a field

around a magnet and he called lines of

force the direction in which a compass

would Point anywhere now we can

illustrate Paradise field by means of an

experiment which probably good many of

you have done with a magnet and IR

filings we've got a magnet under this

table here and you'll remember that any

little piece of iron is turned by the

magnetic field into a magnet so all the

filings I scatter on this table will

become little magnets with North and

South poles and they'll line up in

strings head to tail and show the

direction of paradise's lines of force

watch now while I scatter these filings

you will see how they're feeling the

magnetic field

underneath and now if I tap it a bit to

give them a chance to arrange themselves

I I think we will see Paradise lines of

force coming

out you see it makes quite a pretty

picture of the lines of force around

this

magnet here of course they're only in

two Dimensions we can only see what the

lines are like over this table but

really the lines are spreading from one

pole here to the other in all directions

in

space here I got one of my strong

magnets and a box of these filings with

a lid on

top I pull it up I pull up lid and all

and there you can see perhaps these

filings making little wreaths between

the poles showing the lines of force

going in all Direction between these

poles lastly these iron filings

illustrate in rather a nice way the way

in which a magnet is turned into a

magnet when it's in a magnetic field or

rather I should say when a piece of iron

is not a magnet to start with becomes a

magnet when we put it in a magnetic

field I've got a plain piece of iron

here it's not a magnet at allall I'll

put it underneath the table and stick it

onto the end of this magnet and now if I

tap I think you will see all the lines

of force coming from its

end now wonder now that end is strongly

magnetic you see all the lines of force

coming into it that's of course why my

little steel cylinders all stuck

together well there then are some of the

very simple properties of magnets I hope

in the next talk to go on to some of the

rather more complicated ones

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