How Things Work

The Inner Life of Everyday Machines


By Theodore Gray

Photographs by Nick Mann

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Million-copy bestselling author of The Elements, Molecules, and Reactions Theodore Gray applies his trademark mix of engaging stories, real-time experiments, and stunning photography to the inner workings of machines, big and small, revealing the extraordinary science, beauty, and rich history of everyday things.

Theodore Gray has become a household name among fans, both young and old, of popular science and mechanics. He’s an incorrigible tinkerer with a constant curiosity for how things work. Gray’s readers love how he always brings the perfect combination of know-how, humor, and daring-do to every project or demonstration, be it scientific or mechanical.
In How Things Work he explores the mechanical underpinnings of dozens of types of machines and mechanisms, from the cotton gin to the wristwatch to an industrial loom. Filled with stunning original photographs in Gray’s inimitable style, How Things Work is a must-have exploration of stuff–large and small–for any builder, maker or lover of mechanical things.


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PEOPLE ARE MESSY. They’re complicated and unpredictable. They can hurt you, and sometimes they hurt inside. Machines are not like that. They are what they are. They don’t lie or cheat or turn the screw just when they know it will hurt the most. (Except printers. Printers are the psychopaths of machines.) Machines follow the rules. Even if you don’t understand those rules at first, once you learn them, they will never change. They will remain true and the same, forever and always. This is especially true of machines you make yourself.

Other people’s machines, complex manufactured things, can be frustrating and difficult to master. (Hence the existence of shooting ranges in Las Vegas where you can bring your printer and shoot at it with pistols, assault rifles, sawed-off shotguns… you know, whatever it takes.) But a thing you’ve made yourself is an open book. As you design it and bring it into existence, the machine reveals its nature to you one step at a time. In the end, it exists because of you, and you will always know it better than anyone else. You know not only its final form, but all the roads not taken, the other shapes and ways of being it could have embraced. When a manufactured thing breaks, it can be nearly impossible to fix, but when a machine you made breaks, well, you made it once, you can make it again.

A life built around making things is a good life. When you make things, they become a big part of who you are. And, as you make them, you sometimes find that they in turn are making you.

FOR MANY YEARS I worked on creating a computer program called Mathematica. Many other people worked on it too, but for several years, at the beginning, the Notebook user interface portion of it was mine and mine alone. I found great satisfaction in watching this creation of years come together. It was my life. (Literally: I had no other life, not even a date, for a decade.)

Even today I can see in my mind the structures inside this program, the internal logic, the chaos in a few places. I haven’t looked at the actual code in many years, but if I did, I’m sure I would find many old friends, along with new ones added by the programmers who have come after me.

I still use Mathematica nearly every day to do my work. Yes, sometimes I curse my former self for bugs I could have fixed or features I will never see because no one else will ever care enough to add them. It was my baby, but not anymore. And, like my kids who were once small but then grew up, I have to accept my baby for what it is, not resent it for what it might have been.

Making Mathematica shaped me for twenty-three years. It’s an important thing in the world, and I am proud of my work on it. But I’m also glad that when the chance presented itself to make something else, I took that road.

I got started collecting elements by accident, but have since spent a lot of time with them—I wrote a few books about them. Elements are good. Like kids, they are primal and raw, unique and universal. Everything is made of elements—everything we know and everything we are. And the kids, too, they are made of elements. The machines we call molecules are some of the most intricate and remarkable machines in existence. The machines called DNA and the machines called proteins are life itself to us. The time I spent with elements changed my life, and made me better. More interesting, I think.

I Grew Up with Things

SOFTWARE AND ELEMENTS are great, but this book is not about software or elements. It is about the certain and comfortable world of mechanical things. I made, played with, took apart, broke, and fixed a lot of things when I was young, and in the years since. I learned a lot from these things. Most of all I learned to love them. They changed me. They were there for me in good times and bad. They kept me going, and opened worlds for me. These things are now a part of my past, but other things are very much part of my present, and yours. I have gathered many interesting things for you to see and learn about in this book. I hope that in the pages that follow, you will see the beauty I do in the inanimate, yet very alive world of things.

Read about how I made this thing from scrap roof flashing on here.

This is what a calculator used to look like. I loved these things, and am just barely old enough to remember when a few of them were still actually being used. I’ve kept half a dozen of them. None of these work anymore, but I keep them anyway, and maybe someday I’ll try to bring them back to life.

Remember LP records? I hear they are making a comeback now. This is a briefcase I made specifically for carrying records to parties in case I was ever invited to one, which of course I wasn’t.

Read about this touch-keyboard here.

I made this thing. Then I dropped it.

This was one of the most secret military devices of its day: the Norton bombsight. My dad got one as surplus and I spent hours figuring out how to make its gyroscopes spin. It is a sophisticated mechanical computer designed to calculate the precise moment a bomb should be dropped given the airplane’s altitude and speed, and the wind speed and direction.

I made several animals that my parents kept, for which I am eternally grateful.

When I was seventeen I knitted a regulation Dr. Who scarf. Yes, they published the exact row count for each color of yarn. I was working on this scarf when my dad came into my room to tell me that my sister had just died. I thought I’d always remember the exact color band I was on, but I don’t. Just the sun in the window, the smell in the air, the sound of the door, and the feeling that has no name.

On Christmas break from college in Germany, I showed my grandfather Armin (see here) how to make detached rings on a small improvised wood lathe in his cabin high in the Swiss Alps. Don’t get the wrong idea: he was a professional inventor and his small cabin in the mountains had the most finely appointed personal machine shop I have ever seen, before or since. I got a real thrill when he praised my humble baby rattle–making skills. I still remember his exact words: “Ein rechtes Lehrlingsstück,” spoken in the Swiss dialect and meaning “a fine apprentice’s work.”

I invented this thing for listening to the vibrations of metal objects. It has a magnet mounted behind a fine wire coil, so nearby movement of anything metal will create a current in the coil, which can be picked up and amplified. It’s the same idea as electric guitar pickups, but generalized into a “mechanophone” that you can point at any vibrating mechanical thing. I never actually found a good use for it back then, but during the writing of this book it turned out to be the perfect thing for the sonic scale shown on here! Never throw away any machine or device you’ve made yourself.

The Mechanisms in This Book

IN THIS BOOK you will find chapters on things with clear cases, locks, clocks, scales, and the machines needed to make a potholder from scratch. These topics may seem random—and, OK, the chapter on clear things is indeed a bit random (but totally fun, I promise).

The other chapters, however, are anything but random. They represent ancient and foundational machines that helped us measure our world, secure our place in it, and guide us into the fearfully and wonderfully made world of today. No finite list of inventions can ever be complete, and there are many more I would have liked to write about, but these are a good start. By understanding these mechanisms, you can understand a big part of how the mechanical world works.

Writing this book was an absolute joy, and I hope you get a sense of the pleasure it was to encounter and learn about each and every one of the fine things on this page and the many pages that follow.

CLEAR THINGS: The chapter on clear things may have a lot of modern inventions, but it speaks to the ancient human desire to see inside, to understand, to reveal the inner workings of a thing in your hand. The first machines were simple things with all of the moving parts immediately visible. Clear cases help restore a bit of that old clarity to modern devices.

CLOCKS, the youngest category of devices in this book, are at least 3,500 years old. Of course, back then a clock was not much more than a stick in the ground: a sundial. In the centuries—stretching into millennia—since, clocks have evolved into a fantastic array of clever mechanical and electronic devices. And at a certain moment in 1954, they finally became more accurate than a sundial—more accurate, that is, than the earth itself. Clocks are a microcosm of all things mechanical: inventions of every age, from the wheel to the microchip, have found some application in a clock.

LOCKS as much as 4,000 years old have been found, making them even older than clocks. Apparently people have been trying to steal things since before there was a way to record what time the crime occurred. Secrecy is fundamental to locks. With enough information—the shape of the key, or the numbers of a combination—you can open any lock. This fact makes locks one of the first examples of information-processing equipment. They are tiny computers designed to test whether you are in possession of the secret needed to open them. In the modern age, locks have evaporated into pure information—PIN codes, computer passwords, and elaborate public-key cryptography that enables secure transactions on the internet.

SCALES: Older even than locks are weighing scales, which date to the time of the great pyramids of Egypt, 4,500 years ago. The first and still the most important time things are weighed is when they are sold. Weight is the primary way we define how much of something we have, and therefore how much it should cost. For commerce, scales need to be honest (hard to cheat) but not especially accurate: beyond a fraction of a penny on the dollar, who really cares? But for scientific uses, scales accurate to parts per billion are needed, leading to a series of ever more clever designs. In 2018 a milestone was reached: a scale was built that is able to weigh more accurately than we are able to preserve the weight of the most carefully preserved object in the world, the Standard Kilogram in Paris—which is now no longer the standard of weight.

THE MAKING OF CLOTH: Oldest of all, the tools and skills of weaving and spinning go back to a time before words. As you might expect of something as basic as the way we keep warm, every group of humans for as long as we can know has had some way of making thread or cloth. And when it came time for the great mechanical awakening of the industrial revolution, cloth—cotton in particular—played a central role in both the technology and the politics of the day. The making of cloth guided us into the modern world, and reaches deep into our birth as creatures of hand and eye—back to the time of our becoming not inhabitants but makers of our world.


WHEN I WAS young I saw for the first time a picture of a telephone with a transparent case. You could look inside and see all the electronic components that made it work! My first thought was “wow, that is so cool,” followed by “I want one.” But then I got worried.

A clear telephone seemed obviously superior to every other possible telephone, so why weren’t all telephones made with clear cases? Who could possibly want a phone that hid all the good stuff inside a pointlessly opaque case? I knew it couldn’t cost more to use clear plastic rather than colored plastic. Did the people who made telephones just not realize that they could use clear plastic? Could people smart enough to make a whole telephone really be that dumb? It was at this moment that I realized, with a sense of loss, that maybe not everyone wanted to see inside their telephones. Maybe a lot of people cared more about the color of the case than about how the parts fit together inside it. I’m still sad about this.

I never did get a clear telephone as a kid, and now that I have one, it’s too late to use it: we haven’t had a landline phone connection at my house for years.

Writing a book about how things work is a great excuse to be able to collect a tremendous number of things with clear cases, which are useful for understanding how products are put together. They are also every bit as fun and cool as I imagined they would be. What I did not imagine is that many of them exist only because of prisons.

Some folks who are into electronics, and particularly those who build their own electronic devices, are naturally attracted to clear cases, because they show off the hard work that went into assembling the mechanics inside the device. So it’s not too surprising that soldering irons, USB hubs, and even entire computers are available in this form. Later, we’ll see that this is merely the latest iteration of a trend toward the goal of showing off one’s hard work building mechanical things, a trend that started with clocks over seven hundred years ago.

There may be a lot of people who, for reasons beyond me, prefer opaque plastic cases, but these beauties are proof that I’m not the only one who appreciates how superior a clear case is. These are aftermarket transparent replacement cases for game machines and controllers that allow you to take off and throw away the silly colored shells and replace them with gloriously transparent ones.

You can even get a transparent replacement case for your iPhone, so you can see all the circuitry inside! Well, OK, sorry, this is just a protective case with a photograph of the insides of an iPhone printed on it. But I have gotten double takes from a few people when I use it.

The Transparent Redemption

MY FIRST HINT of the existence of a vast prison-industrial complex of clear objects came when I saw a television much like these two at my friend Koatie’s house some years ago. I thought she was being trendy, but she explained that it was her old prison TV (she used to be trouble). They make them this way so that it’s impossible for convicts to hide drugs, knives, or other forbidden contraband inside the case. Little did I know that this TV was just the tip of the iceberg.

In fact, several brands and styles of old-school CRT (cathode-ray tube) televisions with clear cases were in circulation in prisons for many years. That big gray mass of glass that you see behind the screen is the “tube” part. It’s hollow and opaque, so presumably the perfect place to hide contraband. But actually the tube is filled with a vacuum, so the minute you try to cut a hole in it to hide something, the whole television will violently implode.

A CRT television is full of dangerously high voltages, even days after it’s been unplugged (because the capacitors in its power supply can hold dangerous amounts of charge for quite a while). Turning on a television with its case removed is not a good idea, so it’s really neat to be able to safely see inside one while it’s in operation.

These days, of course, prison TVs are flat-screen, so there’s even less room inside for hiding stuff. And where there had been magnets and high-voltage transformers, now there are only microchips and LCD (liquid crystal display) screens (see here for an explanation of how these screens work).

The back of the flat-screen TV on the previous page.

You can see a similar progression of technology in the wide array of prison radios over the years. The large, discrete components (capacitors, inductors, resistors, transformers, and so on) in the older models have been replaced by microchips in the newer ones. A complete radio these days can exist on a single microchip no bigger than a few breadcrumbs.

As soon as I saw the clear tape player, I thought that the cassettes themselves would make great hiding places for tiny illicit items. They were way ahead of me on that one. The tapes are also clear.

Cassette tapes, remember those? Pretty old-school, but wildly popular in their day, and apparently also in prisons.

Cassette tapes were replaced by CD players.

Clear headphones and earbuds


THIS IS MY all-time favorite clear object, because it combines clockwork and electronic technologies. No batteries necessary here because it employs a hand-crank, wind-up generator.

The generator creates electricity in pulses that come and go many times per second. On average there is enough energy to run the radio, but the circuitry needs steady power, not pulses. A capacitor stores up energy at the peaks of the pulses and releases it during the low points. In this way it smooths out the voltage going to the radio.

In a clever twist, the capacitor also feeds any voltage it accumulates back into the generator, causing it to push back against the force of the spring, slowing down the rate of unwinding. When the sound volume is low and the radio is using only a little power, the capacitor stays charged for quite a while and the generator spins fast only once every few seconds. But when the sound is turned up and the radio needs more power, the generator spins fast all the time.


THIS EXAMPLE OF a clear typewriter is a fascinating hybrid of technologies from different eras: it stands halfway between computer and mechanical device. When you strike the keys, the letters go into a tiny bit of memory on a microchip inside the machine, just enough to store one line of text at a time. You can make corrections to that one line before hitting the Return key, which will trigger the line to print. That’s the computer part. But then the mechanical part takes over: A wheel with lots of spokes, one for each letter and symbol, spins rapidly to position the correct spoke at the top. Then a strong and very fast electronic hammer called a solenoid whacks the spoke, which presses its raised letter onto an ink ribbon layered between the spoke and the paper. An impression of the letter is made on the page.

Although the outside world has moved on to computers, in prisons time has stood still, and clear typewriters, sometimes brand new, still circulate in systems around the country.


A CLEAR HAIR dryer! Not just one but several different models! Finding these particular objects (on eBay and in prison supply catalogs) was the moment I realized that this thing with clear objects went deeper than I’d ever thought possible. If they make clear hair dryers, anything is possible.

Hair dryers are unusual in that they are the only common handheld electrical devices that consume a lot of power. In fact, they are typically set up so that at their highest setting, they draw the maximum amount of power that the electrical code legally allows you to pull from a standard wall socket. If manufacturers could make them to use any more power, they would.

This is the over-temperature safety cutoff switch. It’s a bi-metallic strip, made of two different kinds of metal sandwiched together. When the temperature in the hair dryer goes up, the metal on the bottom expands faster, getting longer more quickly than the metal on top. That makes the strip bend upward when it gets above a certain temperature. That in turn breaks an electrical contact, shutting off the power to the heating coils and preventing the whole thing from melting.

There’s a reason why all normal hair dryers have exactly three heat settings (cool, low, and high), and three fan speed settings (off, low, and high). Power from the wall is AC, which stands for alternating current: it switches back and forth between positive and negative voltage 60 times per second (positive for 1/120 of a second, then negative for the next 1/120 of a second, and so on). It just so happens that there is an extremely cheap, small, and efficient device, called a diode, which allows the flow of electricity in one direction and blocks it in the other.

If you make AC power flow through a diode before it gets to its destination, only half the power (represented by the shaded red area below) will make it through. The low/high power switch in the hair dryer simply patches a diode in or out of the circuit. When the diode is in, only half the power gets through—there’s your low-power mode.

Anything more than two power levels is much more complicated and expensive to achieve. In fact, if you want more than two levels, you might as well go all the way to infinitely variable power, which is done with a device called a triac, found in some expensive hair dryers and in all wall switch light dimmers.

This is what happens if you disable all the safety features in a cheap plastic hair dryer, including the thermal overload switch, the mica heat shield, and the fan motor. It smokes for a few seconds, then melts down around the heating coils. The thing it didn’t do is catch fire, which I’m frankly a little surprised about. I’ve always thought it was inherently unsafe to have a hair dryer made of plastic, but now that I’ve tried really hard to get one to catch fire, I feel a bit better about it.



  • "A stunning coffee-table book with detailed photos. [Author] Theodore Gray explores how everyday things work in great detail, going so far as to build some of them himself, and provides a new perspective on these objects that most of us would never have unless we knew them intimately...What Gray did in his previous books about elements, molecules, and reactions, he has now done for the mechanical systems that run our world, and the result is a beautiful appreciation for systems we all often overlook."—Ars Technica
  • "Another masterpiece."—Boing-Boing

On Sale
Oct 22, 2019
Page Count
256 pages

Theodore Gray

About the Author

Theodore Gray is the author of The ElementsMolecules, and Reactions as well as Theodore Gray's Completely Mad Science, How Things Work, and Engines. He is the creator of the bestselling iPad apps "Elements" and "Molecules," which have both been named App of the Week by Apple, and he was the director of "Disney Animated," also honored by Apple as iPad App of the Year. He co-founded Wolfram Research, Inc., makers of the widely used software Mathematica and the the Wolfram Alpha website. He lives in Urbana, Illinois.

Nick Mann is a photographer specializing in taking beautiful photos of inanimate objects on black backgrounds. His other work includes The ElementsMolecules, ReactionsHow Things Work and Engines. In his other life, he designs and makes specialized note-taking fieldwork equipment and he works in the quality control department for a large automotive company. He lives in Urbana, Illinois.

Learn more about this author

Nick Mann

About the Photographer

Theodore Gray is the author of The Elements, Molecules, and Reactions, as well as Theodore Gray’s Completely Mad Science, and How Things Work. He is the creator of the bestselling iPad apps Elements and Molecules, which have both been named App of the Week by Apple. Gray appeared on stage with Steve Jobs several times in his capacity as a software creator. He also co-founded Wolfram Research, Inc., makers of the widely-used software Mathematica and the Wolfram Alpha website. He lives in Urbana, Illinois.

Nick Mann is a photographer specializing in taking beautiful photos of inanimate objects on black backgrounds. His other work includes Molecules, Reactions and How Things Work. Originally of Urbana, IL, he now lives in Champaign, IL and North Liberty, IA, where he is working towards a geology degree at Cornell College.

Learn more about this photographer