In Our Time - The Microscope

Episode Date: November 28, 2013

Melvyn Bragg and his guests discuss the development of the microscope, an instrument which has revolutionised our knowledge of the world and the organisms that inhabit it. In the seventeenth century the pioneering work of two scientists, the Dutchman Antonie van Leeuwenhoek and Robert Hooke in England, revealed the teeming microscopic world that exists at scales beyond the capabilities of the naked eye. The microscope became an essential component of scientific enquiry by the nineteenth century, but in the 1930s a German physicist, Ernst Ruska, discovered that by using a beam of electrons he could view structures much tinier than was possible using visible light. Today light and electron microscopy are among the most powerful tools at the disposal of modern science, and new techniques are still being developed.With:Jim Bennett Visiting Keeper at the Science Museum in LondonSir Colin Humphreys Professor of Materials Science and Director of Research at the University of CambridgeMichelle Peckham Professor of Cell Biology at the University of LeedsProducer: Thomas Morris.

This BBC podcast is supported by ads outside the UK. Every week, we cover the week's tech news on this week in tech. Hi, this is Leo LePort inviting you to join me and my panelists this week. Jason Heiner, Doc Rock, and Mike Elgin will talk about Anthropics' new AI. They say it's too dangerous to release Sam Altman in response to the firebombing of his house, and Samsung jumps profits eightfold thanks to AI. Hi, you'll find Twitter at twit.tv or wherever you get your podcasts. Thank you for downloading this episode of In Our Time.

For more details about In Our Time and for our terms of use, please go to BBC.co.com.uk slash radio four. I hope you enjoy the program. Hello, one afternoon in January, 1665, Samuel Peep's visited his favorite bookshop and on Impulse bought a volume that took his fancy. On his way home, he stopped off at the butcher for a hare's foot to treat his collic. The following day he wrote in his diary, Before I went to bed, I sat up till two o'clock in my chamber

reading Mr. Hook's microscopical observations, the most ingenious book that ever I read in my life. This work by Robert Hook is commonly known as the Micrographia. It's the earliest book in English containing detailed observations and drawings making use and new and revolutionary use of the scientific instrument, the microscope. Invented around the turn of the 17th century,

the microscope has transformed our understanding, standing of the natural world, making it possible to examine objects far too small to be seen by the naked eye. In the last hundred years, the development of the electron microscope and other discoveries have made it possible to see structures as small as a single atom. We're meant to discuss the history and applications of the microscope. Jim Bennett, visiting keeper at the Science Museum in London. Sir Colin Humphreys, Professor of Materials Science and Director of Research at the University of Cambridge, and Michelle Peckham, Professor of Cell Biology at the University of Leeds. Jim Bennett, various names have been suggested as the inventor of the microscope.

Can you give us some examples of the early essays in this? We have to go back to Middleburg in the Netherlands at the beginning of the 17th century. So the story is rather like the originating story of the telescope. Very similar because the same names are involved. Spectacle makers in Middleburg like Hans Leperche, who's working up optician, Zachari. Janssen also involved a claimant for the early telescope. It's less of a competition, the microscope.

People are less fired up about who did this first. There aren't any patent applications and so on. But the story is very similar, and the names are all quite easily recognizable. Galileo, for instance, is an early player in the microscope as well as the telescope. You can use a Galilean telescope as a low-powered microscope in a particular configuration. Kepler again comes into the story because it's Kepler who makes the first. gives the first theoretical account of the way microscopes might work and the kind of configurations and lenses that you would use. So there are a lot of people interested in this in the early days.

We know of a compound microscope in England in 1619, owned by a Dutchman, an engineer called Cornelius Drevel. And it's England, the Netherlands and Italy, as with the telescope. They're making the play for the development of the microscope in the... in the 17th century. So it's a story that's very familiar to us in a way and yet less fired. Because with the telescope, people are interested in the heavens, cosmology and so on, Galileo's making a big thing of what it all means. People are less anxious about being interested in the very small. But it gets going, one of the people really gets you going, is again, it's a Dutchman, Van Levin Hook. Can you tell us what he did?

that was very important. Yes, it's odd to begin with Leavenhook in a way because he's so unusual. I mean, he's outside this standard practice. By the time Leavenhook's involved in the late 17th century, there are a lot of commercial makers. There are quite a number of microscopists doing interesting things

and doing things with compound microscopes. I say microscopes with more than one lens, with two or perhaps three lenses. Leavenhook is in Delft. He's only speaking Dutch, she says. He doesn't have any other languages. He's working very much in his own. He's a cloth merchant.

He's using a simple microscope. That's a say one with a single lens. It begins as a hobby, but it takes over his life. And he becomes very famous as a microscopist. But what's curious about Levinhoot, these microscopes are so unusual. He's making them himself, he's making tiny little spherical lenses.

He has very short focal length lenses. They have to be used in a very particular way. You hold them right up to your eye because the focal length is so short. And he sees the most extraordinary things, little animals, as he can. calls them everywhere, prosazoa, spermatazor, and so on. The world at the micro level seems to be teeming with life in a way that no one could

have imagined. So it becomes very famous for these spectacular results, which are extraordinarily impressive, but can you really believe them? It's a really very unusual phenomenon that is the practice of Anthony Leavenhue. He's extraordinary industrious. He had 250 optical microscopes he built. He created more than 400 lenses himself, including three in gold. And he didn't publish a book, but he wrote letters to the Royal Society's new publication and thereby became known, famous and copied throughout Europe. Yes, again, it's this Dutch-English access.

And yes, the philosophical transactions, the new journal of the Royal Society, needs content, and he's providing it. Colin Humphreys, almost at the same time, the English scientist Robert Fook was working with earlier. microscopes and I mentioned the book Micrography in my introduction. Can you tell us a bit more about how what he did and how he did it?

Right, so Robert Hook is sometimes called the English father of microscopy in the same way as Lunahook's the father of microscopy and I think he was a genius and this was micrography we've mentioned, it was the first major book the Royal Society published. It was the first scientific bestseller

so the first edition sold out in a few days and I think he was probably the first popularizer of science. So his book showed what you could do in optical microscope. It showed these wonderful images. They were engraved in the book. Images of insects of flies. He had folding

out plates in this book. You can fold out four times. Get these huge magnified images of flies. And people wanted optical microscopes. It popularised optical microscopes. And I've brought along a picture which I think is, to me, the most significant picture. Just what we

need. I know. I know. I'm not very close to the microphone. and we might have a chance. You'll see, yes. And this is a picture which shows little crystals. And when you put little crystals, almost anything under the microscope, they don't look like spheres or blobs. They're usually geometrical shapes.

So they're cubes or pyramids or rhombahedral or something. And so this is a picture of these little crystals. And what's amazing is in this page from Micrographia, he's drawn underneath them these crystals, and then he's put inside each drawing little spheres. and he's shown how the shapes of these crystals, there might be cubes or pyramids, can be made up from these little spheres.

And these little spheres are almost certainly atoms. I think that's what is believing. And so it's not generally realised. I think Robert Hook was the first person to actually say materials of compose of atoms. And he doesn't say it. It's just there in his drawings. And I think that's remarkable.

And he's not known for this. So, you know, I think he's just a great scientist. It's an extraordinary fertile time that Royal Society, wasn't it? We still can't really credit it. that in such a short time, so many great men, I'm afraid, they all were men, produced so much that defined at the modern scientific age. That's right. I mean, his misfortune in the sense is that he was born at the same time as Isaac Newton, and Isaac Newton sort of outshone him, and so everyone knows about Newton,

and people don't know about Hook, but they were both just scientific geniuses. Can you tell us about his microscope compared with Lohenhoek's microscope, the actual object itself? Was it different? I think it was very simple. I mean, Lohenheim made his own lenses, and he was a genius of that, but I think they're just very similar microscopes. And just one very interesting point, Robert Hook coined the word cell. So when he saw blood cells or other sorts of cells, he called themselves. And the reason he did, he could see in his microscope that these were surrounded by membranes.

And they looked like walls in the microscope. And he was such a lateral thinker. He thought, this reminds me of a monk cell. A monk lives in the little room. It's called a cell because it's got walls around it. And so he took this word self and amongst cells, and he coined the phrase cell for biology. And of course, we talk about biological cells all the time today.

We have a professor of cell biology at the time at the moment. Right. From the 18th century, scientists, persons like you, began to notice flaws in microscopes, in particular with their lenses. What was the problem? What was the main problem? The main problem was what was called aberration.

So the lenses were not perfect. And this goes back a long time. I mean, I've got another picture here. I won't show, but it's in the British Museum. I'm going to show. We all love to see. It's it. It is set. So this is in the British Museum. And this is called the Nimrod Lens.

Nimrod Lens. I'm holding it up. Nimrod Lens. And this is 750 BC, right? 750 BC in Syria, now modern Iraq. And this was the lens, and it magnified about three times. And not better than three times because of the aberrations, also used as a burning glass to form fire. and I think why the developed nations, the early civilizations, came from sunny countries,

was because you could use lenses to make fire. You could then smelt bronze and brass and iron, and so the Bronze Age and the Iron Age developed in these sunny countries, because we had lenses, they can make fire. In England, we're still rubbing sticks together to make fire, you know, very difficult. And so they had these lenses, can make fire, and so that's why I think early civilizations were in sunny countries. And so what Leon Hood did was to polish these and polish these

make them much better. But we've moved on from blowing hook, I'm afraid. They began to discover that the light microscopes dependent on light had limitations. Now, can you tell us, quite soon, can you tell us what the major limitation was? The major limitations were the lenses, you can polish spherical lenses, they don't focus a point in the object to a point in the image. They form a blurred image, and that's called an aberration. And the second problem is if you use white light, then although they can focus the individual colours to a point,

when you have white light, they focus the different colours to different planes in the image. You've got a blurred image, and if you look at an image with white light, you get coloured fringes around it, and these are called aberrations, and these limited the performance. Because of the difference of the wavelengths, because of the difference of the wavelength. That's right, yes, yes.

And we can correct those now. But then they couldn't, and this would seem to be a limitation. They couldn't correct them then, but then they could form other lengths. So if you have a convex lens, you can make a concave lens, and that corrects them, and that was done at a third. early early stage, with electron microscopes, we get to later, the correction wasn't done until 1997, right? Very recent corrections. There's another more fundamental limitation which you can't correct, and that's due to the wavelength of light itself. And perhaps...

Well, I'm going to Michel now. At the end of the 18th century, microscopes very much like the microscopes we see today. Will you just talk us through the instrument that had arrived by the end of the 18th century about 120, 130 years after, up to the two prime inventors. Well, I suppose what you could say, it is very much like. Actually, as a child, I had a microscope. It would probably not dissimilar

because I was a bit of a sad person and I wanted to have a microscope for my birthday instead of a doll. Well, that's sad. It sounds good. I think I had a microscope. Well, you know, I too was fascinated at looking at things. And I think the sort of microscope I had

was probably then was not just very dissimilar. So it had a stage that I could put whatever it is I wanted to look at on the stage. It had a little mirror underneath, and I could shine some light on the mirror, so I could illuminate my specimen. Then it's got a tube, and at one end of the tube is the objective lens, and the other end is the eye piece, and you look down the eye piece, and both the objective lens and the eye piece magnify the specimen. So I don't know what I would have had on that microscope,

probably nothing more than about 100 times I would have thought. But at the end of the 18th century, was it? much more developed than that, or did you get as a present when you were a child, the state of the art microscope at the end of the 18th century? Oh no, no, no.

What I got was probably... So what was going on at the end of the 18th? How did it develop? Well, it's not... So that sort of basic compound microscope that Jim was talking about earlier, that's pretty much what you would have had. What you get today is probably not too dissimilar

and the basic components are very similar. It's just a much more chunky microscope instead of a single eye piece, you'd have two eye pieces, so you can have binoculars and stereo vision. You've got a few more, perhaps a few more internal lenses that you never even really know about

as a cell by way, just I have to say, but which will correct for these various aberrations that they're talking about, like the problem with the colours which we call chromatic aberration and so on. Well, can we come to, the German physicist called Ernst Abbe

worked out that in the 18th is that the conventional microscopes, that's just the one you've got, could only be improved up to a point. Now, what was that point? Well, it's what was alluded to earlier, really. So the main problem is that when light goes through a specimen, when you're looking through a specimen,

the light goes through the specimen, and it gets diffracted, which basically means the light bends about, and it forms this fuzzy. So if you've got a nice little... Because light is hitting it at different speeds. Yeah, well, it's a bit more complicated than that. So you've got to...

Can you make it complicated? Okay, so if you think about a normal bright field microscope, you've got white light that you're illuminating your specimen with, which has got multiple colours in. But you've got lots in the object that you're looking at, you've got lots of very small points, if you like, that you're trying to image. So inside a cell, you might be looking at organelles,

you might be trying to look at some detail. And what happens is when the light interacts with those objects, it diffracts, it bends around them, and it will travel at different speeds through the cell, as well. So you get this interference effect as light that goes through the cell and light that doesn't go through the cell that the waves will interfere. And by the time you actually form the image, you get this blurry spots. Instead of the bright, really discrete spot that you might be trying to image, you get a blurry spot. And that's just simply a property of physics.

And this is what Abbey worked out. It basically means that if you've got two little spots in the cell that are very close together, you can't tell how close they are. are, well, sorry, if they're closer than a certain distance, which is roughly about half the wavelength of light, you can't actually distinguish them as two separate spots. You can only see them as one spot, and that's because of this blurring effect.

So it's a property of the light and the wavelength of light. You're limited by the wavelength of light in terms of what you can resolve. This is something called the diffraction limit. So it's about how much detail you can see in a specimen. So if they discovered, the diffraction limit in 1870, they then set about trying to do something about it. How much did they manage to do about it and how soon?

Well, you can't. There's nothing you can do at it. It's a property of light and how it interferes with your specimen. And the only thing what you can do is you can make your lenses a little bit better. So there's something called a numerical aperture for a lens. And if you have a bigger numerical aperture, you can collect more light. And if you can collect more light, you can get more detail. But that's about it.

So, because there's a limit to how big you can make that numerical aperture. So you're limited by the light itself, the wavelength of the light, and the numerical aperture of your lens, which is, depends. That gives you a cone of light that images on your specimen. And those two things together. But you still see quite a lot, in fact, very great deal. You can still see quite a lot. Because biologist at the end of the 9th century,

I'm told, found a way of making small objects much easier to see under the microscope. because of? Is that because of staining? Yeah. Yes. Well, it does happen. I mean, Leavenhook did a bit of staining, so this has quite a long history. Can you tell us what staining is? Well, I see, yes. Well, it's adding a dye of some sort to the specimen. Because if you use light passing through a specimen, it doesn't have much differentiation in the visible change that happens to the light. So you don't see the structure. It's largely, I say, transparent and undifferentiated. So you, the idea is to add a stain, a chemical of some sort, which reacts differentially with the structure that's there and makes it visible.

So you can see these differences that are invisible otherwise. But that's... Is this addressing the problem that Michelle is talking about? Not really. It's a way of... It doesn't get around the diffraction limit in any way. It just makes the... It brings out the... It's rather as though you have a...

You're painting by numbers, let's say, you and you have your basic outline and then you add lots of colour and you differentiate all those different bits by colour and and but that that is happening through the 18th century sometimes accidentally because they're doing other things they're

injecting there's a lot of preparation involved in these specimens and they're injecting fluids into which stained almost by accident then in the 19th century when you have a lot of synthetic dyes at a lot of possibilities for adding stains deliberately and it becomes a whole industry when does this give you that you had

didn't have before. It makes the the structure visible in the specimen so that then at least the possibility of seeing it. So it's got nothing much to do with the optical apparatus that we've been talking about. It's rendering the structure which is in the specimen visible by differential colour. And there are there are whole industries who will prepare the slides for you

by the late 19th century. Colin Humphreys, so we're still on the list. So we're still on the limitations of the light microscope, but in 1897, J.G.O. Thompson at Cambridge discovered the electron. And surprisingly, by these laws of unexpected consequences that always turn up in science, not very much later, it was entering into this field with a scientist called Ernst Rusko, invented what became as known as the electron microscope. Now, can you tell us about the electron microscope and just tell us about it, first of all? Okay, so this is a remarkable series of scientific discoveries that led to the electron microscopes.

As you say, J.J. Thompson discovered the electron in 1897 in Cambridge. First fundamental particle discovered, you know, neutrons and protons and protons afterwards. And then about 20 years later, maybe in 1924, a French scientist Louis de Broilie, he showed, where he theorized, every moving particle has a wavelength associated with it. That was 1924. People thought he was mad. Most people thought this is absolutely crazy. How can a particle be a wave? And some scientists, though, they said, let's do an experiment.

So one year later, in 1925, in England, Thompson and Reed, in America, Govison and Germa, they looked at, one looked at gold, one looked at nickel, they bombarded it with electrons, and they found a diffraction pattern. They found that these solids, diffracted electrons, they bent electrons, as Michel has said, and this shows that the electrons were a wave. And then people, there was a joke at the time, he said, electrons are waves on Monday, Wednesday and Friday. Their particles on Tuesday, Thursday and Saturday,

and on the Sabbath they rest. So that was a nice joke. And so electrons then were known to be waves in 1925. And the question was, could you do anything about this? And a German called Bush found that you could focus electrons because you can't lose glass lenses to focus on the most with light. A magnetic field. So he constructed a magnet with a hole in the centre,

a bit like a polo mint. You pass electron beam through this magnet, it focuses the electrons. Then Ruska said, okay, we can put two electron lenses that got to get an electron microscope. In 1933, he built the first electron microscope with a resolution better than an optical microscope.

Where'd you get your electrons from? To start with, they got them from what were called discharge tubes. They were called cathode discharge tubes. So you ionized a gas, and you had gas ions in the tube, and electrons in the tube. And then you had an anode and a cathode,

and the cathode accelerated these, or the anode accelerated the electrons towards it, had hold in the centre, and you've got a beam for electrons coming out. Can you take us on from that, Michelle Peckham? How would you like me to take it on? Well, as far as you can go, really? I mean, Colin set it up if you just run it in a minute. Okay, all right. Well, I mean, so as I sell by this, we use light and electron microscopes,

and of course the beauty about electron microscopes is electrons have a much shorter wavelength. So what that immediately means, because we know that wavelength limits your resolution. So if you've got a shorter wavelength and the resolution, so that's how close to things can get together. If the wavelength is shorter, you can see things that are closer together. So you get a better resolution. So you get, well, actually, we used to have arguments about this at the dinner table about just how much you could see with a microscope

because my sons would come to me and say, you can see atoms with an electron microscope. And I believe that actually is true now. but the sort of microscope that we use routine is still trying to stay in the 20th 3rdias. This seemed to be a big advance, didn't it? It was and I can give you a very nice example actually from Leeds where if you want to look inside a cell

you can see a certain amount of detail with a light microscope but if you get to the electron microscope you can see much more detail so if we talk about something like a sperm which has a nice phlegalum we want to see what's inside that flagellum that's very narrow you can't really see much inside that with a normal microscope for light microscope, put it in the EM, you can start to see this very beautiful crystalline arrangement of microtubials inside, which are these protein filaments, so little cores of tubulin. So that's why they call microtubules.

And that was discovered by Irene Manton, who was a scientist at Leeds. She was the first woman professor at Leeds, in fact. So she used the electron microscope. She was one of the first people to actually look at, you have to cut thin sections, you have to look in thin sections, but she was able to show this very fine ultrustructure of flagella for the first time. So that's what you can do in an electron microscope,

but you can't do the light microscope. So for a time, Jim Med, these two were running together. The electron had come in, seeming to be sweep everything away. This was the new thing. The microscopes was going to light were old-fashioned passe and didn't do as much as this did. What were the advantages and disavit? As soon as slowed down, they began to weigh up the advantages and disadvantages. Can you briefly tell us the advantages

and disadvantages each of those? Yes, as an historian, I'd want to make a bit more continuity than we've seen so far. I mean, at the moment, the electrons suddenly appear. In order to improve the resolution, sort of problems we've been talking about, you've shorter wavelengths. So, Microsoft will start using

bluer light, and then they start using ultraviolet light, and then they start illuminating after a fashion with electrons which were the wave length associated with electron is even shorter. So there is a continuity here. It isn't quite so abrupt. And that continuity is seen in the practice you were saying, Michelle, that you use both light and electron microscopes. Advantage is, well, the obvious advantage we've heard about for the electron microscope, the resolution is so much, you know, enormously greater, the magnification possibilities are much greater. It's a bit hard to talk about. Disadvantages, except, of course, it's all very expensive.

and there's a lot of skills involved, a lot of investment involved, the preparation of the specimens is very difficult, have to go in a vacuum and so on, and how well they'll stand up to that is an issue. So there's a whole area of expertise that accrues to electron microscopy, which is a possible disadvantage.

One other thing I'd like to say... Why is it so expensive with electron microscopes? Well, because a lot of equipment. but most of us don't know why of course. And you have special rooms and so on. And then you light microphones are developing as well and becoming expensive. There's just one thing I would like to say in relation to what your son was asking about the can we see atoms. There's a big distance now.

I don't know if you'd call this a disadvantage between the natural process of seeing and the manipulation of this experience so that we think of it as seeing. And I don't know if you think of it as seeing. I don't know if you think of that as a, you have to tell a very long story now to the interested public and maybe to as well to yourselves, which is a theoretical story to bring you back into thinking about this

as a visual experience and need to recreate the image out of the electron outcome of the bombardment. And is that a disadvantage because we are so far away and in conceptual terms from where we began this story, that's to say, looking more closely.

Do you want to take that up, but do you want to... Yes, let me talk to... So I think you're true. What we say is correct, in that until very recently, you needed really quite good theory to interpret electrical microscope. I think now, with the very latest electron microscopes,

atoms look like atoms. So you can actually see atoms and you think they do look like atoms. And so it's very vividly. representation now. Can I say with you, Colin, the electron microscope made a significant discovery about metals, which was very important

in the sense of knowledge for knowledge of sake, but also extremely important, it was applied commercially. Right. Can you tell us about that? I'm talking about dislocation. Yes, alright, let me talk about dislocation. Can we do an experiment here? A quick experiment? I've got to... Well, we're... Okay. Is it to do with dislocation?

It is to do with... It's fundamental You picked up something that looks like a flute now, Colin. It's a copper rod. It's a rod of copper, right? And it's about, I don't know, a centimetre thick almost. And a puzzle that people had right back to the night with, why is metal so weak? Because you can calculate how strong metal should be. And this is a circus trick. So if I pass this to Michelle, would like to bend that, Michelle, this may not work. I'm not very yellow there. Oh, it is. Oh, yes, because copper is quite soft.

It's quite soft. So you bend it. Can you bend it more? Right, okay. Michelle is a... Michelle is bending the copper tube. It's now a rather nice up. And of course it's getting harder and harder and more I'm going to. And now Michelle can pass it to Jim, who's got rippling muscles, to bend it back again. Back again? You didn't think you were going to end for this, did you?

It's incredibly hard. Well, I almost done it. Because there was this strong in the circus who bends something like this. And then you say, I'd give someone 10 pounds if they can bend it back and they couldn't. And what happens is, this has got, to start with, this has got a low-density what they're called dislocations. So metals are just a regular array of atoms, but sometimes things go wrong. They're imperfections

of dislocations, and that's why metals are much weaker than they should be. So what happened? So what happened here is when you bent it, you were creating lots of dislocations, they tangled up, and so when you try to bend it back again, then you know, all tangled up. But the strength of materials is due to dislocations. How did the

electron microscope deal with this? Right, exactly. So the question is, now, that's your question, so I'll get your question. Good idea. Thank you. So in 1950, in 1950s, Peter Hirsch, a visionary scientist at Cambridge, he said, let's have a new research student called Mike Whelan, and he set him this problem.

He said, can you image dislocations in an electron microscope? And they've been proposed theoretically in 1930, and a lot of people didn't believe in them. And so Mike Wynne had the problem and making very thin foils. And so he went to a gold beater where he existed in England. beaten gold, beaten gold foils, and he got beaten gold foils very narrow, very thin, and then he constructed his own equipment to make holes in these. He looked around the edge of the holes, put them in the microscope,

and he saw dislocations there. Which were? What are dislocations? Dislocations are a missing half-plane. If you think of a crystal of being a periodic array of atoms, and you can think of these atoms lying on planes in the crystal, a dislocation is a missing half-plane of atoms. And this makes it weaker than it should be? And this makes it much weak and it should be.

Why? Because if you think of trying to slide a rug over a floor, for example, a heavy rug, and you pull the rug at one end, it's quite hard to get it across. If you want to move it more easily, you form a little ruck at one end of the rug, and you move that rug along, and then you move the rug along into a wrong rack. And that's what happens with dislocations. A dislocations are missing half-plains, like a rock in a crystal, and when you try and deform it, it can move easily. And what consequences did this have?

And this means that metals are much weaker than they should be. And we understand now why they're much weaker. And if you want to make them stronger, you put lots of dislocations in which tangle up inside the crystal. And so the strength of materials were explained by the electron microscope. This is a fundamental breakthrough. Excellent. Michelle Pekam, in the 1950s we have light microscope, as it were, doesn't make a comeback. It's never been out.

It's developed into something called phase contrast microscope. What does that do and why is that a development? Okay, so well, the face contrast was invented by Zernica in about the 1930s, something like that. And the problem is that when you illuminate a, if you're trying to look at a cell down a microscope, it's actually not got very much contrast in it because it's mostly water with a few proteins in it. And that doesn't give you a lot of contrast, hence the dyes and so on that we've talked about before. So if you really want to see some detail, there's a little trick you can do because, As I've said before, the light that goes through the cell

travels slightly slower than the light that doesn't go through the cell and they interfere when they come out the other side and rejoin, as I were. So if you can somehow accentuate that difference and increase the delay between the light that goes through the cell and the light that doesn't go through the cell, you can get more interference between those two different paths of light. So that means you get more interference. So you have to think about waves on a pond, making little ripples.

if you've got two waves and upon that meet each other and the ripples can actually, where they're in phase, you get bigger ripples and where they're out of phase, you get smaller ripples. So you accentuate the difference between the two different wavelengths when they're out of phase. And what that does in the microscope is it gives you better contrast. So now you can see much more detail

because without using stones, you can see detail. And that means that you can look at live cells. Because live cells, you can see them with bright feel, but there's not very much contrast. but if you put some contrast in with this face contrast, then you can look at live cells. So somebody called Abercrombie, for example, made very good use of that.

This is in the old days where you didn't have fancy cameras or anything like that. So you had a film camera, and he set that up on his microscope, and he was imaging the cells as they're moving about, and he discovered this very important thing called contact inhibition. So if two cells meet each other,

they're ruffling away, they meet each other. The ruffles stop, and then the cells move away again. Two cancer cells meet each other They don't care One will climb over the other And they just really don't have that contact inhibition So he made this very important discovery About how cells interact with each other

And how that's affected in cancer cells By that ability of using phase contrast To be able to see cells in more detail And see the outlines of cells and so on Jim Bennett Is this as the light microscope The microscope works through light Is this a sort of beginning of more development

that have happened in the last 50 years, 50, 60 years? I guess so. It certainly sounds like it to me. It isn't something I know much about the last 50 years. But certainly... Yes, certainly as fierce contrast business. And confocal techniques as well. I know a little bit of Biden,

and that's, again, a technique of the last... Well, certainly the last few decades. Sort of took off in the 80s. Yeah. So, yes, it's interesting. The light microscope, has far from disappeared from the repertoire of equipment in the way one might have expected. Can I go back to our magician from Cambridge on the left?

Colin Humphreys, the first electron microscopes have manufactured were all of one type. They were called transmission electron microscopes. And then a different model was developed. Can you tell us what it was and what it can do? Yes, sir, this different microscope was developed in Cambridge. So UK had a lot of influence here. This is called a scanning electron microscope. which was developed by engineering laboratory and came by Charles Oatley.

And for some materials, you really want to look at surfaces. So, for example, if you look at Velcro, how does Velcro work? You want to look at the surface of Velcro, see these little hooks in the Velcro. Or if you want to look at an optical disk, which is a bit like an old-fashioned 78 gramophone record, but an optical disk which has lots of grooves in it. So you want to look at the surface. And what Charles Oatley did, he focused a beam of electrons, onto the surface of material

and then he scanned it across the surface and he detected the electrons back scattered from the surface and displayed those on a screen. It's a bit like a television screen is made up of an electron beam scanning across the television screen giving different intensity and different colours and so this is what a scanning electron microscope

does it. They're enabled to have a magnified image of the surface. When they were first made, they were made by Cambridge scientific instruments they thought they'd sell six instruments, thousands of reuse, particularly in industry, also universities. It's like an optical microscope.

It gives you bigger magnification. Look at surfaces. Incredibly useful instrument. Another breakthrough in the 1950s, Michelle Peckham, was the development of a new technique known as immunoflorance. Immunophorescence. I beg forrestes. I beg for instance, pardon.

Immunophorescence. Yeah, so immunophrases is interesting because actually Fresad dies have been around for quite a long time. But really the big breakthrough, I guess, was actually developing antibodies, because now what you can do is, so when you look at a cell, you can just see everything. If you want to look at some particular protein,

do you get something really specific that you're interested in? You've got to be able to label that specifically, and that's, of course, where antibodies came in, so you can stick your antibody onto your protein of interest and then find out where it is in the cell by attaching a fluorescent dye. So that sort of brought a new type of microscopy called epiphorrescence microscopy where you shine fluorescent light onto your specimen

and you collect a fluorescent light back. all fluorescent materials, you excite them at a shorter wavelength and they emit it a longer wavelength. And this takes you towards what? What is better about it? What does it give you that you didn't have before? Well, it's revolutionary because now that you... So, for example, I was talking about the microtubules earlier. If you want to know how those microtubules are organised inside a cell, you could only really perhaps use the EM to do that.

And the problem with the EM, what we haven't mentioned is that you can't look at live cells in the EM at all because it's all under vacuum and cells just die. and you have to fix the cells and sign. But you can look at cells, you can actually look at mass and substructure in cells simply by staining up the only bits that you want to look at. And as long as that's within the resolution, you can look at things like microchubules,

so you can see how they're organised in a cell without having to go to electro-microscopes. So the other advantage is you don't have to do any sectioning because you need very thin specimens for your LEM. So you can look at the whole cell. You can look at the organisation of all the microtubules, and actually it's rather beautiful, I have to say, particularly in dividing cells are my favourite.

Jim, can I come to Jim now? It seemed for a while that the electron microscope is going to simply replace the, completely replace the old-fashioned light microscope, but that didn't happen. Can you tell us what the state of play between the two is now? Well, as I understand it, there are horses for courses.

I mean, there are some things that electron microscopes can do and light microscopes can't. And after all, for a lot of everyday work, the light microscope is the everyday tool. And that's always been, or that hasn't always been the case, that's been the case from the late 19th century. And we're talking here about the cutting edge of university research and so on, but there are labs across the world in hospitals and so on

and filled with high part, it's true, but light microscopes that are working, not in theory, not dissimilarly from those of the middle of the 19th century. And so these microscopes have been developed, The lenses are being developed and the techniques of reading from them have being developed also. It's interesting. And if you think about the 19th century, for example, I mean, I'm a historian, so I'll always think of parallels in the past. The light microscope was being developed in an exaggerated way by the fellows of the Royal Microscopical Society.

They were wealthy amateurs who were pushing the light microscope as far as they could. And they were more interested in microscopes than in the science that the microscope might reveal. So they developed microscopes that really weren't much use for the everyday working scientist. So that balance between the cutting edge of research and the everyday needs of professionals has often created a kind of tension in where you put your scientific resource. And that was very exaggerated in the 19th century. As I understand it, we've got that more into balance now, but maybe the scientists can tell me whether that tension still exists.

I just can talk to physics. Well, quite. For example. Colin Humphrey's, can you give us a little indication before, can you give us some idea of the way in which the electron microscope has driven technological research and development? Well, yes, so life today, as we know, just wouldn't be possible without the discoveries with the electron microscope.

So, for example, silicon chips, which gets smaller and smaller and smaller. To start with, you can see the size of the circuits in an logical microscope, and they got smaller. The electron microscope is essential to see what you've done with the silicon ships, so to design silicon chips. So all our computers, composed of silicon chips, impossible without the electron microscope that development. Our mobile phones, full of silicon chips,

gasoline chips, impossible without the electron microscope. Even Rolls-Royce jet engines, and now that particles in these turbine blaze, you know. So modern life depends on the discoveries for the electron microscope. It's just the remarkable. One of the most amazing things about science is, Thompson in Cambridge discovers, as it were, and names and works out the electron.

and a chap getting on with being a Cambridge Don and being on being a thinker, pure researcher, and not much later it's running the world. It is remarkable, yes. These developments which people think may have no consequences. It's like Faraday said, electricity will never be used and, you know, we use it everywhere. Yes. Although they are, the electron microscope has great, there are great difficulties, apart from the expense, aren't they? Yes, I mean, they are much more complicated to often.

and you do have to take a lot of care with how you prepare your specimens for the microscopes and so on. I mean, you can do a lot of that. I mean, I think they have revolution biology as well simply because of what you can see, but also for actually looking at molecules, proteins and so on. You can get some very high resolution structures of things by using the, you know, you can do it. It's just a lot more work. Well, while we've got you here, we talked about the diffraction limit earlier. was thought to limit the improvement of light manuscripts

but scientists seem to have found a way of breaking through that limit. Yeah, so I think it's been the last five to ten years of light microscopy have a bit of a revolution. So I think we all got very frustrated with the light microscope. So the first thing that came along was GFP and that means you can tag your proteins with this green fluorescent protein and that was what the Nobel Prize was awarded for a few years ago. What that has been developed in and what people,

realises that if you've got a fluorescent object in the cell, which you can't actually tell whether it's a bunch of objects together because they're too close together for you to be able to resolve it or just one object, if you could actually take, say, those 50 fluorescent molecules in that object you're trying to visualize, but switch them on one by one by one, then you can actually work out where each of those molecules is. And then it's a bit like sort of picture by dots. If you can actually see the dots one by one, then you can break the resolution limit. You haven't really broken the resolution. limit. What you're doing is a trick that you're just switching the molecules on in time one by

one by one and then finding out where each of the molecules is and then adding them all back together to form the object. So that's one of the ways in which super resolutions come about. And that's through, first leaf through GFP because somebody may, so Jennifer Lippincott-Schawson American made a GFP that you can switch off and switch on photoactivator or GFP. So you shines some light on it. It's dark, shines some light on it, it appears. And if you can switch your molecules on one by one by one, you can see where they are. So it's not really breaking the limit. It's just position. It's positioning the molecules.

There is one other technique where you can. We haven't got to come back for that. Thank you very much. It's the first time this studio has been a surgery because you came here with a terrific cough when you haven't coughed. Well, that was all down to the tablet. It wasn't the tablets. It was getting engaged in the conversation. Thank you, Michelle. Pekam, Jim Bennett and Colin Humphreys. Next week, Hindu creation stories.

Thanks for listening. There are many more Radio 4, arts and disciplines. discussion programs to download for free. Find these on the website at BBC.co.uk slash radio four.