I am holding probably the most amazing piece of metal that you have seen in any of our videos.
This is the original mirror from Isaac Newton's first telescope
and this is his actual first telescope that he made.
You can see behind it is the drawings that he made
and the description he wrote in Latin of this telescope
So
this telescope
has been with the Royal Society
since 1688.
There was a bit of interruption, where it was,
where it went to an instrument maker
so there may be some later additions,
but there is absolutely no doubt
that this mirror is the original mirror.
If I was a physicist
I'd be telling you about the
wonders of this telescope
and the advantage of using a
mirror over lenses
so you get the images.
But I'm going to tell you
about the metal of the mirror
and the mirror is made from a metal
that is called speculum.
Speculum is not an element,
it's an alloy;
a mixture of metals
and
it's a mixture
of tin and copper.
Now you can see the problem straight away
if you're making a mirror
to look at stars and things
is that copper is coloured;
it's red,
or reddish colour.
And for a really good mirror
you need to have it absolutely colourless
so you see the actual colours of whatever is in space.
The moon looks the right colour.
It just happens that if you mix
two parts of copper with one part of tin
and just put in a little amount of arsenic,
and obviously I am not in the lab so I haven't got any arsenic here,
you can get a metal which has been known for
perhaps a couple of thousand years called speculum,
which gives you a really nice mirror finish.
Speculum is the Latin word for a mirror
[BRADY]: That's not a very good mirror
[PROF POLIAKOFF]: Well, when it was first made it would have been polished
and it would have been really good and
you can still see the traces of its polishing.
So what's amazing about this
is how heavy the metal is.
Copper is quite a dense metal
and so is tin so this is much heavier
than the modern mirrors that you would have, which are made out of aluminium, which is very light.
And this mirror fits in the back here
so the light comes into there
onto the mirror and back again
and here is the eye piece so you look in there.
And if you look at Isaac Newton's drawing here
you can see there is a picture of his eye.
I don't know whether this is Isaac Newton's eye or somebody else's.
So you can see here is a large ball,
which is quite a clever mount,
that allows you to turn the telescope in whatever direction you want.
And I was quite mystified because
there is a little crown down here
and
I wondered why on Earth in a telescope you should need a crown.
And our librarian explained to me
that Newton tested his telescope
by looking at some architectural feature in Cambridge
on another building,
and
here is an indication
that he drew to show the magnification;
how much bigger the image was,
and this is what it looked like to the naked eye,
and here is what it looked like through his telescope.
So it really worked
I just think it's extraordinary
that I should be touching something
that Isaac Newton should have made himself.
But
to come back to the chemistry
it is really very interesting
that one of the key features of this telescope
was having the right material to make the mirror because
if you couldn't make the mirror, nothing else is important.
And so
right at the heart of this fundamental development
in physics
was a bit of chemistry.
It turns out that you have to be quite clever in making this alloy,
because if you put too much copper then it's red,
and surprisingly if you put too much tin it's a bit blue.
So there is a rather nice sweet spot
which, depending how much arsenic you put in,
gives you just the right mixture
so that the surface reflects colours
faithfully and doesn't absorb anywhere in the visible spectrum.
I'm not a metallurgist, but very often
quite small amounts of added material
can affect the way that metals crystallise
and the way that it crystallises then affects its surface properties
and hence affects the way that it reflects light.