Speaker 1: Welcome to Stuff to Blow Your Mind production of My
Speaker 1: Heart Radio. Hey you welcome to Stuff to Blow Your Mind.
Speaker 1: My name is Robert Lamb and I'm Joe McCormick. And
Speaker 1: in today's episode, we're going to be looking at a
Speaker 1: spectacular bit of hypothetical air travel that has intrigued us
Speaker 1: for centuries. The vacuum airship or knull ship as I've
Speaker 1: seen it referred, and that's such a cool name for
Speaker 1: something that I think I had to front loaded on
Speaker 1: this episode, but usually it's just referred to as a
Speaker 1: vacuum airship. And the basic principle, as we'll discuss, is
Speaker 1: pretty simple. Hydrogen, helium or hot air filled balloons allow
Speaker 1: an airship to traverse the skies because these gases are
Speaker 1: lighter than the surrounding air, and even lighter gas is
Speaker 1: the absence of any gas at all, the vacuum. If
Speaker 1: one could create a vacuum chamber or bladder that was
Speaker 1: itself light enough, then this could be used to provide
Speaker 1: lift for airships on Earth or even on other planets.
Speaker 1: I mean, it's such an obvious extension of the idea
Speaker 1: underlying balloons indirigibles all lighter than air flight craft. You
Speaker 1: would have to assume that if if you don't see
Speaker 1: things like this being used all the time, there must
Speaker 1: be a pretty good reason. And I guess we'll get
Speaker 1: to that in a little bit. But yeah, it's it's
Speaker 1: like an obvious place to take the idea. Yeah, yeah,
Speaker 1: And and so it's ultimately such a fascinating topic because yeah,
Speaker 1: there's the basic underlying science of the principles of it
Speaker 1: are pretty sound. There are material challenges in place, but
Speaker 1: then the history of the concept is pretty interesting as well.
Speaker 1: Thus far, however, the main place you'll see these vacuum
Speaker 1: airships deployed are going to be within the pages of
Speaker 1: science fiction and fantasy. And one of the main examples
Speaker 1: of this and this and you'll see this why le
Speaker 1: Cited is a novel that was serialized between nine thirty
Speaker 1: by Edgar Rice Burrows titled Tarzan at the Earth's Core,
Speaker 1: not to be confused with At the Earth's Core, which
Speaker 1: was his nineteen fourteen novel that established the hollow Earth
Speaker 1: world of Pellucidar, which is this, like it sounds, it's
Speaker 1: like a world within our world. It it has a
Speaker 1: race of intelligent and I think psychic terra Saar overlords
Speaker 1: called the Mahar or the Mahar and the that novel
Speaker 1: prominently features a subderine. So we've actually mentioned that book
Speaker 1: on the show before in our episode about subderines, which
Speaker 1: is another sort of fantastic um hypothetical, uh, means of
Speaker 1: traversing the natural environment. But this Tarzan at the Earth
Speaker 1: score is a crossover novel which features Tarzan traveling to
Speaker 1: the inner world v a vacuum airship. And I had
Speaker 1: to dive into this in a little bit. I assume
Speaker 1: you haven't read this one either. No, I haven't read it.
Speaker 1: I do remember it was mentioned in that earlier episode.
Speaker 1: But also it just got me thinking about, like, wait,
Speaker 1: where do all of these science fiction books about a
Speaker 1: hollow earth with like a different biosphere or or some
Speaker 1: kind of archaic state. Uh, where does all that come from?
Speaker 1: Because this isn't the first one. This is in what thirty,
Speaker 1: but like as far back as the eighteen sixties you
Speaker 1: had Jules Verne with Journey to the Center of the Earth,
Speaker 1: which is very similar concept. I don't think it has
Speaker 1: like psychic pterosaurs, but it does have a hollow earth
Speaker 1: with like essentially a mirror biosphere on the inside that
Speaker 1: has dinosaurs and other prehistoric creatures. Well, it makes me
Speaker 1: think we should come back into a proper episode on
Speaker 1: the concept of the hollow Earth. You know why why
Speaker 1: it it wouldn't work A quiet individuals thought that it
Speaker 1: could have worked, and why it has uh, you know
Speaker 1: why it has captivated people's imagination for so long. Yeah,
Speaker 1: I don't know of anything older than than Jules Verne,
Speaker 1: but but there may be. So I had not read
Speaker 1: this book either. I think the only Edgar Rice Burrows
Speaker 1: novel that I have read is one called The Monster Men,
Speaker 1: which memory serves is largely it seems very inspired by
Speaker 1: the Island of Dr Moreau, but it was it was
Speaker 1: pretty fun, as I remember it, And so I went
Speaker 1: ahead and and dove into this one, and I was
Speaker 1: like reading through it trying to find some good examples
Speaker 1: of them talking about vacuum airships. And I think I
Speaker 1: wasted a good, uh like minutes just scanning through the
Speaker 1: book trying to do some searches. And then I realized
Speaker 1: that I was looking at the wrong one. I was
Speaker 1: looking at the Earth's Core instead of Tarzan at the
Speaker 1: Earth's Core. But I switched to the correct book, and
Speaker 1: they talk about the vacuum airship a lot in that one,
Speaker 1: So I can't just find like the one spot where
Speaker 1: they're talking about it there. It's a frequent topic of conversation.
Speaker 1: But I do want to read just a fragment here
Speaker 1: from it where they touch on it. Uh. So this
Speaker 1: is Edgar Rice Burrows from Tarzan at the Earth Score
Speaker 1: again from ninety. The greatest risk that we would have
Speaker 1: to face would be a possible inability to return to
Speaker 1: the outer crust owing to the depletion of our helium
Speaker 1: gas that might be made necessary by the maneuvering of
Speaker 1: the ship. But that is only the same chance of
Speaker 1: life or death that every explorer and scientific investigator must
Speaker 1: be willing to assume in the prosecution of his labors.
Speaker 1: If it were but possible to build a whole sufficiently
Speaker 1: light and at the same time sufficiently strong to withstand
Speaker 1: atmospheric pressure, we could dispense with both the dangerous hydrogen
Speaker 1: gas and the rare and expensive helium gas, and have
Speaker 1: the assurance of the utmost safety and maximum of buoyancy
Speaker 1: in a ship supported entirely by vacuum tanks. Perhaps even
Speaker 1: that is possible, said Tarzan, who was now evincing increasing
Speaker 1: interest in Gridley's proposition, the Americans shook his head. It
Speaker 1: may be possible someday, he said, but not at present
Speaker 1: with any known material. Any receptacle having sufficient strength to
Speaker 1: withstand the atmospheric pressure upon a vacuum would have a
Speaker 1: weight far too great for the vacuum to lift. Okay,
Speaker 1: so first of all, I am definitely picturing this as
Speaker 1: the Kristoff Lambart Tarzan from from gray Stoke. This has
Speaker 1: got to be it, right, Yes, yes, it's it's a
Speaker 1: gentleman Tarzan here. Mild spoiler for the for the book.
Speaker 1: Obviously they figure it out. I believe some sort of
Speaker 1: rare element or metal is introduced that it makes the
Speaker 1: impossible possible, because otherwise, how are you gonna get Tarzan
Speaker 1: to the Inner Earth to battle psychic terra stars. I mean,
Speaker 1: it's funny how this Psychic Terrastar book does uh correctly
Speaker 1: diagnose some of the problems with existing lighter than air craft.
Speaker 1: So one problem is needing to have continued access to
Speaker 1: your lighter than air gas so that so that you
Speaker 1: can like refill the balloon or the tank do because
Speaker 1: there's always going to be some kind of leakage or
Speaker 1: potentially even damage that would allow the gas to escape.
Speaker 1: You'd have to have a way to get more helium
Speaker 1: in there. If it's helium. Of course, if it's hydrogen,
Speaker 1: you run into a whole uh raft of other problems,
Speaker 1: as one can see with the history of the henden
Speaker 1: Bergens and fourth hydrogen very flammable and having the same
Speaker 1: uh you know, fixed access problems as helium. But yeah,
Speaker 1: with with a vacuum like, you don't need to carry
Speaker 1: vacuum around with you. All you would need to do
Speaker 1: is find a way to pump out the chamber. Yeah,
Speaker 1: so you can see why it's such an attractive option.
Speaker 1: And this this passage kind of encapsulates all that I
Speaker 1: was looking around too. I noticed that it's It's been
Speaker 1: noted that at least two other authors that we've mentioned
Speaker 1: on the show before have also employed vacuum airship principles.
Speaker 1: Peter Wattson makes use of them in his Rifters books
Speaker 1: as a means of enabling flying machines. I totally forgotten
Speaker 1: about this, and then Ian in Banks invoked them in
Speaker 1: at least three different novels, including at least one that
Speaker 1: I definitely read, but I also don't remember mentioned of them.
Speaker 1: I guess I just wasn't My mind wasn't as open
Speaker 1: of the idea of vacuum airships when I was reading
Speaker 1: these books. And I've also read that they factor into
Speaker 1: Neil Stevens since The Diamond Age, which I have not read,
Speaker 1: but I've heard good things about. So wait a minute,
Speaker 1: I actually know almost nothing about Tarzan. Where old does
Speaker 1: Tarzan go? Is he like the lepre Con or like
Speaker 1: he goes to space, he goes to the to the ocean,
Speaker 1: he goes to the Hollow Earth? Does he does he
Speaker 1: go to Las Vegas at some point? What? What? What
Speaker 1: are all his adventures? Well, Joe, there are twenty four
Speaker 1: Tarzan novels by bar Rice Burrow, so you know he
Speaker 1: he ultimately gets around. I have not read any of them,
Speaker 1: but you can just when you when you start scanning
Speaker 1: the titles, you realize that he maybe starts running out
Speaker 1: of jungle and he has to has to go to
Speaker 1: lost Empires in the Earth's core, in a city of gold,
Speaker 1: forbidden City. Uh. Looks like he may join the Foreign
Speaker 1: Legion at one point, so, uh, you know, he's got
Speaker 1: to get out there and travel around and and explore
Speaker 1: the outer world. But I think generally speaking, he's always
Speaker 1: going to battle or befriends some sort of the large animal.
Speaker 1: Thank you for correcting my tarzan ignorance. Now I know,
Speaker 1: all right, But I guess before we go any further
Speaker 1: exploring the history of proposals for vacuum airships, it would
Speaker 1: be worth briefly explaining the underlying reasoning, and that is that,
Speaker 1: whether you're talking about a lighter than air gas inside
Speaker 1: a balloon or a rigid chamber containing a vacuum, the
Speaker 1: physics phenomenon that would cause this, uh, this balloon or
Speaker 1: or chamber to fly is what's known as Archimedes principle,
Speaker 1: named after the ancient Greek inventor and mathematician. And I
Speaker 1: think the core idea you really need to understand in
Speaker 1: order to grasp Archimedes principle at a gut level is
Speaker 1: the idea of fluid displacement. Fluid displacement so a few
Speaker 1: extreme experimental conditions aside. Basically, if you are on Earth,
Speaker 1: you are submerged within a fluid. So if you're a
Speaker 1: barracuda or a jellyfish, that fluid is going to be water.
Speaker 1: If you are a human standing in line at King
Speaker 1: that fluid is the atmosphere. Both gases and liquids are
Speaker 1: fluids because they both flow to fill containing environments. And
Speaker 1: when you occupy space within a mass of either kind
Speaker 1: of fluid, whether it's liquid or gas, you are taking
Speaker 1: up space that this fluid would otherwise fill, would otherwise
Speaker 1: rush in to fill, So, in other words, you are
Speaker 1: displacing gas or liquid. The inside about physics that our
Speaker 1: comedes had is that objects submerged within a fluid are
Speaker 1: pushed upward, meaning in the opposite direction of gravity, by
Speaker 1: a force that is equal to the weight of the
Speaker 1: fluid displaced by that object. And this is why boats float.
Speaker 1: I mean, humans have been making boats for a long time,
Speaker 1: but uh, it took us a while to figure out
Speaker 1: what is the exact physics principle governing the flotation of boats.
Speaker 1: So a boat, for example, may have a steel hull,
Speaker 1: and steel is very dense, So you would think that
Speaker 1: a steel boat should sink, right, I remember wondering about
Speaker 1: this when I was a little kid. How does you
Speaker 1: know metal sink? So how does a metal boat float?
Speaker 1: A metal boat floats because the hull of the boat
Speaker 1: displaces a lot of water. An amount of water that
Speaker 1: is as heavy as the boat itself. So when a
Speaker 1: boat gets launched out into the ocean, it sinks down
Speaker 1: in the water until the amount of water it displaces
Speaker 1: is the same as the weight of the boat overall.
Speaker 1: And then after it reaches this equilibrium, it's held up
Speaker 1: on the surface of the water by that buoyancy, that
Speaker 1: force pushing upward on the boat equivalent to the weight
Speaker 1: of the water it displaces. And this, of course is
Speaker 1: also why a ship sinks when water leaks into its hull.
Speaker 1: It's water that is denser than air filling that void
Speaker 1: that was otherwise filled with with air. So kind of weird,
Speaker 1: but I think accurate. Way to think of a ship
Speaker 1: on the ocean is a rigid balloon filled with air. Now,
Speaker 1: the same principles that apply in water also hold true
Speaker 1: in the fluid of the atmosphere. Is a force pushing
Speaker 1: up on an object that is equivalent to the weight
Speaker 1: of the air that that object displaces. Now, for most
Speaker 1: objects around us, the the atmospheric buoyancy is negligible because
Speaker 1: objects are way more dense than the atmosphere that they're displacing. Uh.
Speaker 1: Though technically it is true that your body has a
Speaker 1: measurable buoyancy within the air. It's not enough to make
Speaker 1: you float up off the ground, because you know, human
Speaker 1: bodies are are pretty massive. But based on some rough
Speaker 1: calculations I looked up, it seems like it's probably a
Speaker 1: fraction of a pound at sea level for the typical
Speaker 1: range of human body weight. It's one estimate I saw
Speaker 1: was that it's like zero point two pounds for a
Speaker 1: hundred and seventy pound adult. So how can you change
Speaker 1: an object in order to take advantage of that atmospheric
Speaker 1: buoyancy and make it float up in the atmosphere like
Speaker 1: a boat floats on the water. Well, as demonstrated by
Speaker 1: balloons and dirigibles, what you can do is make that
Speaker 1: object take up a lot of space, mostly with material
Speaker 1: that is lighter than the atmosphere itself, which is usually
Speaker 1: going to be a lighter than air gas like hydrogen
Speaker 1: or helium. But of course it could also be a
Speaker 1: chamber that has no gas in it at all, nothing
Speaker 1: in it at all, which would be the lightest possible
Speaker 1: way of taking up space. Now here's a weird fact.
Speaker 1: I was just wondering about which of the fundamental forces
Speaker 1: actually causes the force of buoyancy. Where is that force
Speaker 1: pushing up on a boat or pushing up on a
Speaker 1: balloon coming from? Counterintuitively, that force originates with gravity, which
Speaker 1: is kind of strange because the force of buoyancy is
Speaker 1: going in the opposite direction of gravity. Right, Why would
Speaker 1: gravity cause something to rise up from the ground instead
Speaker 1: of sinking down? But you have to think about a
Speaker 1: sort of chain of causes here. So, whether you're talking
Speaker 1: about the atmosphere or the ocean, gravity is pulling all
Speaker 1: that fluid toward the Earth's center of mass. It's pull
Speaker 1: ling all the water or the gas down. So gravity
Speaker 1: is the cause of air pressure and water pressure, and
Speaker 1: it is the downward pressure of the surrounding fluid that
Speaker 1: causes buoyant objects within that fluid to rise. So, to
Speaker 1: use some kind of approximate and anthropomorphic terms, when a
Speaker 1: balloon floats, it's because the heavier gas of the atmosphere
Speaker 1: around it is all rushing down to get to the surface,
Speaker 1: and it has to push the balloon out of the
Speaker 1: way to get there. And it can push the balloon
Speaker 1: out of the way because the balloon is less dense
Speaker 1: than it is. It's kind of like if asking, well, hey,
Speaker 1: I'm why if everybody's trying to get to the TV
Speaker 1: section of the big box store on Black Friday, everybody's
Speaker 1: trying to get there, then why is the four Why
Speaker 1: am I being pushed out of the store because everybody
Speaker 1: else is pushing harder than you are. Thank But to
Speaker 1: come to real world proposals for vacuum airships. Uh. One
Speaker 1: thing I was shocked about was how far back this
Speaker 1: idea goes. I would have imagined it was something dreamed
Speaker 1: up in the nineteenth century. Yeah, I was very much
Speaker 1: the same. But then I started looking into it, and
Speaker 1: sure enough, the roots go all the way back to
Speaker 1: the seventeenth century. So our story here begins with an
Speaker 1: Italian Jesuit priest by the name of Francesco Lana Detersi,
Speaker 1: who lived sixty one through six seven, sometimes called the
Speaker 1: father of arionnautics. His groundbreaking book from sixteen seventy, titled
Speaker 1: Prodromo de larte Mastra, was apparently the first to discuss
Speaker 1: the possibility of human flight via mathematical calculations and an
Speaker 1: understanding of physics. Uh. These were no mere loss speculations either.
Speaker 1: This was a work that was translated and then circulated
Speaker 1: throughout Europe, and subsequent advancements in ballooning, for example, are
Speaker 1: are often directly linked to this work, namely thinking of
Speaker 1: the month Gaffier Brothers a flight in seventeen eighty three,
Speaker 1: which was an unmanned balloon flight lasting about ten minutes. Now,
Speaker 1: I want to stress we're largely talking with with the
Speaker 1: Western and European sphere of of exploration here. If you
Speaker 1: get into the Eastern accounts, there are some some older
Speaker 1: accounts of possible you know, unmanned hot air balloon experimentation
Speaker 1: in China for example, going back you know to I
Speaker 1: think like the third century see wow, but again unmanned. Now,
Speaker 1: in this particular book, Lana covered many subjects uh here
Speaker 1: and I was reading about this in a paper titled
Speaker 1: the Jesuit Contribution to Written Art Technological Sources in the
Speaker 1: seventeen and eighteen centuries by Karina Gramatki from sixteen. Apparently
Speaker 1: the topics include invention itself, drawing, design, pigments, chemistry, medicine, arithmetic,
Speaker 1: the production of telescopes, microscopes, and finally aeronautics. Pick a lane.
Speaker 1: I mean, this was an age where yeah, if you
Speaker 1: were if you were into stuff, you were you were
Speaker 1: into everything. Yeah, so, um a particular interest to Lana
Speaker 1: here though we were recent advancements in the creation of
Speaker 1: the vacuum pump. This would of course been a continuation
Speaker 1: of suction pump technology. Uh. The idea of the vacuum pump.
Speaker 1: The first vacuum pump was invented in sixteen fifty by
Speaker 1: the German scientists Otto von Garrick and subsequently experimented on
Speaker 1: by others. Oh. Yeah, we've talked about Otto von guerricky
Speaker 1: before in I think in an episode that we did
Speaker 1: about atmospheric pressure, specifically reference to his experiments with the
Speaker 1: so called Magdeburg hemispheres, which was a really interesting experiment
Speaker 1: that took place in the sixteen fifties, I believe, And uh,
Speaker 1: it's been while since we talked about it, so I
Speaker 1: may be forgetting some of the details, but basically, from
Speaker 1: what I recall, they took two brass hemispheres half spheres,
Speaker 1: and then greased the edges of them with lard and
Speaker 1: then pressed them together and then used the invention of
Speaker 1: the air pump to remove air from inside these two hemispheres,
Speaker 1: creating a vacuum within of course, a partial vacuum. You know,
Speaker 1: they're not going to get every single molecule out, but yeah,
Speaker 1: they're getting getting most of the gas out of them.
Speaker 1: And then they hooked these hemispheres up to horses and
Speaker 1: had the horses pull in opposite directions to try to
Speaker 1: pull them apart, and they couldn't. Like that, even horses
Speaker 1: could not separate them. What they were demonstrating there was
Speaker 1: how heavy the atmosphere is. That when you take all
Speaker 1: of the atmosphere out of the inside of these two
Speaker 1: two half spheres, you create such a disequilibrium that the
Speaker 1: you know, the atmosphere is essentially reaching down and and
Speaker 1: uh clutching these two things and pressing them together so
Speaker 1: that even great force cannot pull them apart. Yeah. There
Speaker 1: there are a couple of papers on this topic that
Speaker 1: I was reading from New Scientists actually, like I was
Speaker 1: kind of getting the impression that maybe the editor at
Speaker 1: New Scientists is like pounding the desk that I need
Speaker 1: more vacuum airship stories. But one of them was from
Speaker 1: two thousand and nine by Paul Collins titled The Rise
Speaker 1: and Fall of the Metal Airship, which is ultimately about
Speaker 1: metal airships in general and not just the vacuum airship concept,
Speaker 1: but he mentions, uh this this experiment, writing uh quote
Speaker 1: Otto von Gerriki had drawn together small copper hemispheres with
Speaker 1: such a strong vacuum that teams of horses could not
Speaker 1: pull them apart. But he mentioned some other things of
Speaker 1: note here. Collins also writes that the concept of a
Speaker 1: vacuum airship appears in a German interplanetary travelog of seventy four,
Speaker 1: envisioning trips to Mars. So another example of something ultimately
Speaker 1: far earlier than I would have had, oh guessed it.
Speaker 1: If I was to guess, well, when when we were
Speaker 1: people first thinking about vacuum airships in the atmosphere of Mars,
Speaker 1: I would not have gone with the mid Uh. Now
Speaker 1: is a brief detour. I want to touch on another
Speaker 1: thing that Collins mentions here um to get to the
Speaker 1: title of his paper, there actually was eventually a metal
Speaker 1: non vacuum airship, and this was in the first one
Speaker 1: was a thirty eight meter airship designed by David Schwartz
Speaker 1: and helped into the sky by the Prussian airship Battalion.
Speaker 1: And it was a It was blimp shaped, but its
Speaker 1: skin was riveted aluminum plates, and it traveled about six
Speaker 1: kilometers total before it stopped. They put the brakes on
Speaker 1: and it caused the thing to crumble due to its
Speaker 1: rigid construction. But the advantage of a fully functional metal
Speaker 1: airship would be speed. Though so uh the the idea
Speaker 1: didn't go completely away, and in good years, original airship
Speaker 1: designer Ralph Ubson quote formed the Metal Clad Airship Corporation
Speaker 1: to build an aluminum clad helium airship, the z m
Speaker 1: C two for the U. S. Navy. Although notoriously difficult
Speaker 1: to handle, the quote unquote tin bubble, as it was dubbed,
Speaker 1: could reach a speed of a hundred kilometers an hour,
Speaker 1: and it put in twenty two hundred flight hours before
Speaker 1: it was decommissioned in n and that was it for
Speaker 1: metal airships. That was the last one that took to
Speaker 1: the skies here on Earth. And yet that was the
Speaker 1: Detroit z m C two Angel. I include a picture
Speaker 1: of it here for you. If one was looking at
Speaker 1: you might not guess that what you're looking at is
Speaker 1: is a metal structure, aluminum clad helium airship. That I mean,
Speaker 1: if I've ever seen a tin bubble, that is the
Speaker 1: tin bubble. But to clarify again, the one the actual
Speaker 1: examples we've just been talking about, the people got up
Speaker 1: in the air flying even if they were even if
Speaker 1: they failed early on, these were not vacuum airships. These
Speaker 1: were airships that you even though they had rigid out
Speaker 1: or hulls, they did use some form of gas inside. Yeah. Yeah,
Speaker 1: So ultimately, as as we'll discuss, the vacuum airship is
Speaker 1: still a concept that individuals are still chasing today. Now
Speaker 1: coming back to Lana's book here, another important connection here
Speaker 1: would be to Robert Boyle's work proving that air has weight. Essentially,
Speaker 1: it was proven that all of the atmosphere could be
Speaker 1: mechanically drawn out of a volume. Maybe the nature didn't
Speaker 1: abhor a vacuum quite as much as previously supposed, and
Speaker 1: Lana has taken the next step by speculating one exciting
Speaker 1: way that such a vacuum could be made to work
Speaker 1: for us. So what Lana does here is he basically
Speaker 1: applies what was known at the time regarding the nature
Speaker 1: of air, vacuum and cylinders to devise a means by
Speaker 1: which first vacuum spheres would be made that would float
Speaker 1: up through the air, and secondly that with enough vacuum
Speaker 1: you could also float a vessel. So he proposed a
Speaker 1: vessel consisting of a basket with a say ill and rudder,
Speaker 1: held aloft by four large twenty five ft spheres made
Speaker 1: of thin copper sheeting and bound together by rigging. Uh.
Speaker 1: This was of course never actually built, but there have
Speaker 1: been various illustrations of what this would have looked like.
Speaker 1: I included one here for you, Joe. It looks positively whimsical.
Speaker 1: Why does it? Does it have an oar? I guess
Speaker 1: that's some kind of rudder. Actually, yeah, this is some
Speaker 1: sort of rudder device to steer it. Though it really
Speaker 1: does look like a paddle for the air. Now again,
Speaker 1: now again, Atlanta was a very serious individual, so it
Speaker 1: is he's not just dreaming here. He's applying what was
Speaker 1: known about about the atmosphere and you know, current understanding
Speaker 1: of physics, and so he was. He was serious about
Speaker 1: the underlying principles at work here. So he discusses not
Speaker 1: only how this concept might work, but he also gets
Speaker 1: into some of the objections to it. For instance, do
Speaker 1: you might ask, well, wouldn't this just float up into
Speaker 1: outer space until the people aboard died and it would
Speaker 1: just be completely uncontrollable. Well, he describes how controlling the
Speaker 1: air vacuum levels would allow you to make adjustments and
Speaker 1: keep yourself from just floating up to heights altitudes beyond
Speaker 1: which you had intention of traveling to. Right, So, I
Speaker 1: guess the fear is that, you know, if the vacuum
Speaker 1: is potent enough that it would just float you up
Speaker 1: to the top of the atmosphere and you'd sit on
Speaker 1: it like a boat floats on top of the water. Now,
Speaker 1: of course, you have to remember that even though a
Speaker 1: vacuum chamber would have buoyancy within the atmosphere, it also
Speaker 1: again there is weight, you know, there is weight made
Speaker 1: up of the shell surrounding the chamber and the boat
Speaker 1: and all that. So that would counterbalance that to some extent.
Speaker 1: But then also, yeah, the other thing is that you
Speaker 1: could control altitude just by allowing some amount of gas
Speaker 1: back into these partial vacuum chambers, and then so that
Speaker 1: would help you sink back down and then if you
Speaker 1: want to float up again, you would once again pump
Speaker 1: that gas out. Yeah. Now, the big problem here, of course,
Speaker 1: is the notion of containing that vacuum um. The big
Speaker 1: question would be wouldn't it crush the copper spheres that
Speaker 1: are contained that vacuum, or you know, that are allowing
Speaker 1: the whole system to supposedly float to begin with. And
Speaker 1: the correct answer we know now is yes, it would
Speaker 1: have just crushed those spears. But at the time Lanta
Speaker 1: contended that, now, this is the perfect shape of the
Speaker 1: sphere would hold up to the equal pressure of the
Speaker 1: vacuum within it. Again, we know now this wouldn't work,
Speaker 1: but his hypothesis was that it could possibly function. Right,
Speaker 1: So I guess here you're you're getting into the idea
Speaker 1: of a balancing act, right, so that you can, of
Speaker 1: course create a pretty pretty strong vacuum within a sealed
Speaker 1: chamber without the weight of the atmosphere crushing it, just
Speaker 1: you know, turn smashing that chamber like a tin can.
Speaker 1: But in order to do that, you have to make
Speaker 1: the outsides of the chamber pretty darn strong. And in
Speaker 1: order to make them that strong, you have to add
Speaker 1: more and more weight to the chamber, thus counteracting the
Speaker 1: buoyancy effect of the vacuum within. Right, So you're chasing
Speaker 1: the buoyancy here, and can you achieve it without adding
Speaker 1: so much metal that you lose any buoyancy? You might
Speaker 1: be seeking after and can you can you make the
Speaker 1: materials thin enough without just causing it to collapse anyway,
Speaker 1: And this will remain important when we get into subsequent
Speaker 1: attempts to make this hypothesis and a reality. But here's
Speaker 1: another little bit of of interesting, ultimately speculation by Atlanta
Speaker 1: on the use of aerial technology, because he ends up
Speaker 1: concluding in the book that God would never allow such
Speaker 1: a vessel to actually be built, as it could then
Speaker 1: be used to attack cities and towns from above, and
Speaker 1: that there would be absolutely no stopping such vessels. So
Speaker 1: you know, God would just shut that down. It would
Speaker 1: be like a tower of of battle situation. Oh, this
Speaker 1: theological prediction must have been very well vindicated then when
Speaker 1: when later people came along, I think Leibniz was one
Speaker 1: of them, uh, showing that like no materials we know
Speaker 1: about are strong enough to make this work. Yeah. But
Speaker 1: but but again this idea of of of aerial dominance
Speaker 1: say that would be possible in a military a situation.
Speaker 1: To a large extent line, it was correct here about
Speaker 1: just how devastating this would be. Because, of course, during
Speaker 1: War War one, Zeppelin served as the world's first long
Speaker 1: range bombers, though their dominance would be short lived due
Speaker 1: to their their weakness versus interceptor aircraft, but aerial bombardment
Speaker 1: would indeed be a defining factor of warfare from the
Speaker 1: twentieth century onward. Yeah, the invention of air power, I
Speaker 1: guess I'd say air power, along with like long range artillery,
Speaker 1: completely changed war in the twentieth century. Now, on that note,
Speaker 1: let's move to the next chapter in our history of
Speaker 1: of the vacuum airship or our pursuit of the vacuum airship,
Speaker 1: because this will take us to the late nineteenth century
Speaker 1: right up until the dawn of the twentieth century. Because
Speaker 1: there was at least one spirited individual who thought, yes,
Speaker 1: the vacuum airship can work, and it will work. And
Speaker 1: that is one author, Debase set Uh. And this is
Speaker 1: detailed in Balloons to Jets, A Century of Aeronautics and
Speaker 1: Illinois by one Howard L. Scame Horn. So author debossit
Speaker 1: here was a Chicago doctor who quote designed and electrically
Speaker 1: powered vacuum tub balloon which he intended to use for
Speaker 1: transporting passengers and freight over vast distances at high speeds.
Speaker 1: And this is described as an air tight tube cone
Speaker 1: shaped at either end, and it was going to be
Speaker 1: made of thin steel sheets and it would stay aloft
Speaker 1: when all of the air had been pumped out of it.
Speaker 1: And again it would be used for high speed transportation
Speaker 1: of passengers and freight presumably, uh, you know, from Chicago
Speaker 1: to two other important cities. I mean, if you can
Speaker 1: create that without the atmosphere crushing it, good on you.
Speaker 1: But I am doubtful. Yeah. But and so at this
Speaker 1: point you might think, Okay, Chicago doctor daydreaming about his airships.
Speaker 1: Well know, h he went a step further or uh,
Speaker 1: the good doctor actually organized a company with three associates,
Speaker 1: the Aerial Navigation Company of Chicago, and they raised a
Speaker 1: hundred and thirty thousand dollars at the time through the
Speaker 1: sale of stock to construct one of the ships. So
Speaker 1: already it's sounding a bit more like a legitimate effort now, right.
Speaker 1: And there's more. Uh, When they hadn't produced anything with
Speaker 1: it with these funds, they turned to Congress for more funds,
Speaker 1: and funding bills were introduced in both houses of Congress
Speaker 1: by then a representative Ransom W. Dunham of Chicago, And
Speaker 1: it was apparently some traction or momentum here, but both
Speaker 1: bills failed to pass. Why does this sound like something
Speaker 1: that should be associated with the Chicago World's Fair. I
Speaker 1: know I was thinking the same thing, you know, and
Speaker 1: I guess to a certain extent, we are talking about,
Speaker 1: you know, some of the same sort of you know, futuristic, technological,
Speaker 1: um optimistic ideas that were circulating at the time. You
Speaker 1: know that, like, well, we have the technology, but we
Speaker 1: can do this. We can make these airships a reality,
Speaker 1: and they're gonna fundamentally change the way we travel and
Speaker 1: the way we move cargo. It's this is great, Let's
Speaker 1: do it. Let's get the funding. Okay, well maybe we
Speaker 1: need a little more funding. Let's get Congress on the Horn.
Speaker 1: Uh yeah, it really it sounds like there should be
Speaker 1: a chapter about the Vacuum airship and Devil in the
Speaker 1: White City. Yeah, so skame Horn rights that The fight
Speaker 1: for the Chicago Void vessel here went on for a
Speaker 1: good twenty years up until the dawn of the New century,
Speaker 1: with the Debausit trying in vain to raise enough money
Speaker 1: to build one of these ships, all the while dealing
Speaker 1: with scientific critics that he had just insisted would be
Speaker 1: proved wrong if they would just let him build one.
Speaker 1: He was like, look, just just fund it. Just let
Speaker 1: me build one, and then you'll see you'll see that
Speaker 1: this this is possible. Um, but it sounds like the
Speaker 1: real nail in the coffin. Was that one of a
Speaker 1: couple of leading US aeronautical authorities of the time, Octave
Speaker 1: Channeux and uh Alvary France's zomb quote publicly denounced and
Speaker 1: mathematically prove the fallacy of the vacuum principle. Now, I
Speaker 1: don't know the basis of the fallacy they're talking about there,
Speaker 1: but I would have to assume that again, it's going
Speaker 1: to be, uh, it's going to be rooted in the
Speaker 1: lack of a material strong enough and light enough to
Speaker 1: create this kind of vacuum shell. That if you're going
Speaker 1: to create a rigid shell to contain a vacuum, the
Speaker 1: atmosphere is always going to crush it unless you make
Speaker 1: it so thick and so heavy that it that it
Speaker 1: again out does the buoyancy effect of the vacuum and
Speaker 1: makes it unable to fly. Right. Yeah, I mean that's
Speaker 1: that has always been and still is largely the achilles
Speaker 1: heel of the whole concept. Um by the way. The
Speaker 1: same book also reveals that during this same time period
Speaker 1: there was at least one other Illinois based inventor trying
Speaker 1: to raise funds for an airship. It wasn't a vacuum airship,
Speaker 1: but still airships were very much on the brain. And
Speaker 1: it does sound like, yeah, the people of the White
Speaker 1: City at the time, Uh, we're sharing some of the
Speaker 1: same dreams for what the future of air travel looked like.
Speaker 1: What if H. H. Holmes, instead of operating like a
Speaker 1: a murder hotel, had operated a murder airship. Well, now
Speaker 1: you've got a good movie, pitch. We haven't had a
Speaker 1: I don't think we've had a good airship movie recently, right,
Speaker 1: it could be all like a haunted airship or yeah,
Speaker 1: a murder airship. I can't think of one. I think
Speaker 1: of that scene in Indiana Jones and the Last Cersae.
Speaker 1: That's about it. Yeah, yeah, there was there was another one.
Speaker 1: Or when he when he punches the Nazi out of
Speaker 1: the window no ticket, Yeah, yeah, yeah, there's a and
Speaker 1: that had some some very neat scenes with with the
Speaker 1: Zeppelin there there was also a movie called Zeppelin that
Speaker 1: had Michael Yorke in it. This would have come out
Speaker 1: and I remember seeing bits of it. I don't think
Speaker 1: I've watched it in its entirety, but I remember catching
Speaker 1: bits of it. I'm like American movie Classics or something,
Speaker 1: and and being impressed by some of the scenes of
Speaker 1: people aboard these these airships. Than all right, well, let's
Speaker 1: take things into the twenty one century. Another New Scientist article. Again,
Speaker 1: New Scientist is your go to place for articles about
Speaker 1: vacuum airships. Uh. Noted science writer Philip Ball discussed this
Speaker 1: in in a New Scientist article titled flying on Empty
Speaker 1: from and as Ball discusses, yeah, this idea has never
Speaker 1: quite gone away, in part because if it could be
Speaker 1: pulled off again, you don't need hot air or flammable
Speaker 1: hydrogen or precious helium to keep the ship afloat. It's
Speaker 1: not about pump putting something in. It's about just taking
Speaker 1: atmosphere out. And if you could only figure out the
Speaker 1: materials problem, then you know the world is your oyster.
Speaker 1: And again, the materials problem is designing an outer shell
Speaker 1: that would be strong enough to withstand the atmospheric pressure
Speaker 1: trying to crush it in, but also light enough to
Speaker 1: stay afloat. Right, And of course, as we get into
Speaker 1: the modern era. We're in this age of of of
Speaker 1: special you know, nanomaterials and new ways of looking at
Speaker 1: how these materials can be put together. And of course
Speaker 1: this is this has led to a number of ideas
Speaker 1: that haven't been possible yet. We've been able to look
Speaker 1: to the future and say, well, what what might we
Speaker 1: be able to do If we can just create something
Speaker 1: that's strong and flexible enough, you know, space elevators can
Speaker 1: become a reality then, as well as things potentially like
Speaker 1: the vacuum airship. And so Ball mentions an individual by
Speaker 1: the name of Ben Jenet, who at the time of
Speaker 1: publication was working on his doctorate at the Massachusetts Institute
Speaker 1: of Technologies Center for Bits and Atoms, and Jenet devised
Speaker 1: the use of lightweight quote unquote lattice materials to make
Speaker 1: the shell of a vacuum ship possible. So Ball points out,
Speaker 1: the Genet calculated that even with currently available materials, a
Speaker 1: shell with a thickness one tenth of the radius of
Speaker 1: the sphere it contains will be able to withstand the
Speaker 1: air pressure without buckling, and this would then have to
Speaker 1: be covered with a thin, impermetable skin. Uh Genet's idea
Speaker 1: would also involves creating the vacuum at a higher altitude,
Speaker 1: which I thought was interesting where air pressure is lower,
Speaker 1: and so you would have some I think what it
Speaker 1: was discussed here is solar powered hot air would be
Speaker 1: used to allow the vessel to rise up to that
Speaker 1: initial altitude, and then you would begin the vacuum process
Speaker 1: when it's easier to pull that off, and then you
Speaker 1: would have would have a theoretical operating altitude of something
Speaker 1: like twenty meters or sixty thousand, six sixteen feet. Okay,
Speaker 1: so that makes sense. Up at a higher altitude, the
Speaker 1: air pressure is going to be reduced, which means there's
Speaker 1: less crushing force on the outside of the chamber. Yeah. Yeah,
Speaker 1: that's that's my understanding here. So Ball points out the
Speaker 1: Genet and his collaborators here were in at least we're
Speaker 1: in prep still are in contact with Boeing, so Aurora
Speaker 1: Flight Sciences on the concept, and then an Italian company
Speaker 1: called oh Boot was also looking into vacuum ship ideas.
Speaker 1: Ball reported that while most of the emphasis was on
Speaker 1: shipping with these modern concepts, the idea of at least
Speaker 1: some level of human travel wasn't beyond possibilities as well.
Speaker 1: At least for short jaunts. And again you come back
Speaker 1: to this sort of the the romanticism of airships. I
Speaker 1: can imagine where this would be the case. Well, one
Speaker 1: thing you mentioned that operating altitude you said, twenty thousand
Speaker 1: meters or like sixty feet, is well above the normal
Speaker 1: operating altitude of fixed wing aircraft. So so I wonder what,
Speaker 1: what does what does it look like once you get
Speaker 1: up that high? Are you starting to get into like
Speaker 1: looking at seeing the curve of the Earth territory? I
Speaker 1: don't know. Yeah, it sounds like a situation where you
Speaker 1: you could easily get into this area where you're pretty
Speaker 1: selling the tickets to celebrities and so forth, kind of
Speaker 1: like we've seen with with these other high altitude flight
Speaker 1: near space travel scenarios. So I don't know. It would
Speaker 1: be interesting to see where where things go in the
Speaker 1: decades ahead. But I wouldn't be surprised at all, uh
Speaker 1: to see one of these concepts sort of come to
Speaker 1: fruition in at least in that uh, that scenario. But
Speaker 1: I know when it happens, I'll be able to turn
Speaker 1: to New Scientist to read an article about it for
Speaker 1: all your null ship needs. Yes, So One thing I
Speaker 1: looked into is that vacuum airships have also been proposed
Speaker 1: in various ways for exploring other planets, particularly Mars. I
Speaker 1: think there have been a few ideas along these lines,
Speaker 1: but the main one I was reading about was linked
Speaker 1: to a U T. Austin aerospace engineering professor named John
Speaker 1: Paul Clark, who I think until just recently was here
Speaker 1: in town at Georgia Tech. But Clark and colleagues UH
Speaker 1: submitted a paper that I saw published under the NASA
Speaker 1: Innovative Advanced Concepts Program, or in i a C. This
Speaker 1: was a Phase one proposal called Evacuated Airship for Mars missions.
Speaker 1: And I was reading about this in another summary that
Speaker 1: Clarke had prepared that's hosted on the NASA website, and
Speaker 1: he makes some interesting points. One funny thing is that
Speaker 1: advanced project briefs like this always have the obligatory section
Speaker 1: where they rag on whatever technology we're currently using. So
Speaker 1: this one takes a few good wax at ground based
Speaker 1: rovers on Mars. It's like, you know, we're over with wheels,
Speaker 1: can fall in a ditch, get stuck, you know, and
Speaker 1: it's got limited line of sight, can't see over mountains,
Speaker 1: a lot of problems with with ground based rovers. You
Speaker 1: know what would be better a rover that could fly,
Speaker 1: But of course it's going to be very hard to
Speaker 1: fly on Mars. And here's where a vacuum airship could
Speaker 1: come in. Obviously, a vacuum airship would be useful in
Speaker 1: planetary explorations for some of the same reasons it would
Speaker 1: be useful on Earth. You get the general transportation efficiency
Speaker 1: benefits of air travel without having to rely lie on
Speaker 1: a fixed supply of low density gas like hydrogen or helium.
Speaker 1: To keep a vacuum airship afloat, you don't need a
Speaker 1: supply of gas. Technically, all you need is power power
Speaker 1: like electricity to operate a pump that will continuously evacuate
Speaker 1: gas particles from the inner void. Now, Clark points out
Speaker 1: that there is a good reason what we've never developed
Speaker 1: a vacuum airship for use on Earth. It's the same
Speaker 1: reason we've been talking about already. There is no homogeneous
Speaker 1: material yet discovered that is strong enough to be completely
Speaker 1: evacuated and withstand the crushing pressure of Earth's atmosphere, at
Speaker 1: least not without the structure becoming too heavy to float
Speaker 1: Earth's There is cruel to vacuum airships. But Clark argues that,
Speaker 1: based on his team's calculations, not only is this not
Speaker 1: true on Mars, the atmosphere of Mars is kind of
Speaker 1: an ideal environment for a vacuum airship. Now this immediately
Speaker 1: went against my into sans because before I really reasoned
Speaker 1: it through and read the argument here, I would have thought, well, okay,
Speaker 1: the atmosphere of Mars is much less dense than Earth's atmosphere. Uh,
Speaker 1: the average surface density is something like zero point zero
Speaker 1: two kilograms per cubic meter. Compare that to Earth's, which
Speaker 1: is more like one point two kilograms per cubic meter.
Speaker 1: So Earth's is a couple of orders of magnitude greater
Speaker 1: in density than the Martian atmosphere. Martian atmosphere is very thin,
Speaker 1: and of course a balloon floats by having contents that
Speaker 1: are less dense than the atmosphere. So in an atmosphere
Speaker 1: with lower basically in a thinner atmosphere, I would have
Speaker 1: assumed it's got to be harder for a balloon to float.
Speaker 1: But here is where I would have been wrong. Of Course,
Speaker 1: a vacuum is always less dense than even a very
Speaker 1: thin atmosphere. So if it can be contained and it
Speaker 1: displaces more atmosphere than the weight of the craft itself
Speaker 1: than the weight of the shell and the payload, it
Speaker 1: will float. The real benefit of Martian atmosphere is in
Speaker 1: its pressure to density ratio, so the main constituent of
Speaker 1: Martian air is carbon dioxide. Unlike on Earth, which has
Speaker 1: mainly nitrogen and oxygen. At a molecular level, carbon dioxide
Speaker 1: is denser than nitrogen and oxygen, and the cold temperatures
Speaker 1: on Mars also help make that CEO two even denser.
Speaker 1: You're probably familiar with the idea that hot gas expands,
Speaker 1: cold gas contracts, and yet at the same time, a
Speaker 1: cool advantage of Mars is that there is far less
Speaker 1: atmospheric pressure pressing on the outer shell of the airship,
Speaker 1: so you should be able to construct a vacuum envelope
Speaker 1: that can stand up to the weight of the atmosphere
Speaker 1: on Mars without buckling, using a design that is still
Speaker 1: light enough to float. To read a section from the
Speaker 1: n I a C Paper quote, Mars having the most
Speaker 1: suitable atmosphere for the vacuum airship is quite remarkable, since
Speaker 1: the martiantmosphere is a severe detriment to all other flight
Speaker 1: vehicle designs. So you know you try to do like
Speaker 1: a fixed wing aircraft on Mars, that that's going to
Speaker 1: be really hard. Continuing the quote, the Martian atmosphere is
Speaker 1: comprised almost entirely of carbon dioxide, so vehicles cannot use
Speaker 1: typical combustion fuels which require an atmospheric oxidizer. Glider, plane
Speaker 1: and helicopter designs are all hindered by the atmosphere of
Speaker 1: Mars due to the low Reynolds number and relatively low density. Additionally,
Speaker 1: the vacuum airship provides benefit over other airship designs and
Speaker 1: super pressure balloons because of the inherent robustness of the design. Moreover,
Speaker 1: if damage is sustained, the vacuum airship can land be
Speaker 1: repaired and then re evacuate to resume operation, whereas another
Speaker 1: airship would need to be refilled with a lighter than
Speaker 1: air gas. Therefore, the evacuated airship design thrives in an
Speaker 1: environment where most other aircraft are added disadvantage, and in
Speaker 1: this paper, Clark and colleagues claimed to have already modeled
Speaker 1: the design that should be able to carry a payload
Speaker 1: of fives in Martian air and UH and that way,
Speaker 1: they say could be increased with further design improvements. So
Speaker 1: the argument here is that not only is it a
Speaker 1: situation where to make uh, to make our vacuum airship
Speaker 1: dreams possible, we must go to Mars, it's instead, no,
Speaker 1: that makes this the concept that makes this the design
Speaker 1: that makes the most sense on Mars if we're going
Speaker 1: to have anything flying around, right, that's their argument. And
Speaker 1: I don't know if this has ever made it beyond
Speaker 1: this this phase one or phase two proposal level. So
Speaker 1: I'm not aware of any evidence that this is actually
Speaker 1: like being developed for Mars missions. But at least the
Speaker 1: initial case they make is really interesting, and I wonder
Speaker 1: if if anybody's going anywhere else with it, But yeah,
Speaker 1: I'm certainly intrigued. So Earth, with its thick atmosphere, may
Speaker 1: well hate vacuum airships. It may just forever crush them.
Speaker 1: Maybe there's no way we could really design one that
Speaker 1: would would feasibly work on Earth, but Mars maybe a
Speaker 1: completely different story that that thinner atmosphere. Maybe just the
Speaker 1: place to make the stream of reality. Now, of course,
Speaker 1: this this all brings to mind a previous episode of
Speaker 1: the show that we did titled airships over Venus, which
Speaker 1: discusses the the hypothetical use of airships in the opper
Speaker 1: atmosphere of Venus, at least for unmanned craft, but also
Speaker 1: in some of the more extreme and in fantastic concepts
Speaker 1: that have been discussed in some of the literature, the
Speaker 1: idea that you could potentially have a human being travel
Speaker 1: to the upper atmosphere of Venus and be inside especially
Speaker 1: designed airship. I think one of the ideas for for
Speaker 1: crude aircrafts there is literally that you could have the
Speaker 1: crew inside the balloon because in the Venusian atmosphere, breathable
Speaker 1: air floats. Yeah. Now, looking around, I noticed that there
Speaker 1: there have been some papers that have come out, uh,
Speaker 1: speculating about the use of vacuum airships in the Venusian atmosphere,
Speaker 1: the upper atmosphere. So it looks like there there at
Speaker 1: least are some individuals out there who are thinking about
Speaker 1: taking the vacuum concept to the upper atmosphere of Venus
Speaker 1: as well. You just hope it doesn't sink. I talk
Speaker 1: about heavy, heavy, crushing atmospheres, yes, yeah, the Venusian atmosphere
Speaker 1: ultimately is is an atmosphere that crushes everything all right. Well,
Speaker 1: on that note, we're gonna go and close out this episode,
Speaker 1: but we'd love to hear from everyone out there if
Speaker 1: you have thoughts on vacuum airships or just airships in general. Uh,
Speaker 1: some of these uh, these these concepts we've discussed regarding
Speaker 1: the atmospheres of other worlds. Everything is fair game, right in,
Speaker 1: let us know what you think. We'd love to hear
Speaker 1: from you. As always, Core episodes of Stuff to Blow
Speaker 1: Your Mind, the podcast we found in the Stuff to
Speaker 1: Blow Your Mind podcast. Feed Core episodes on two season Thursdays,
Speaker 1: Listener Mail on Monday's short form Artifact or Monster Fact
Speaker 1: on Wednesdays, and on Fridays, we do Weird How Cinema.
Speaker 1: That is our time to set aside most serious concerns
Speaker 1: and just talk about a strange film. Huge thanks as
Speaker 1: always to our excellent audio producer Seth Nicholas Johnson. If
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Speaker 1: feedback on this episode or any other, to suggest topic
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