How to Invent Everything: A Survival Guide for the Stranded Time Traveler

by Ryan North

We will make electricity so cheap that only the rich will burn candles. —You (also, Thomas Edison)

The real magic comes when you change the number of coils in your outgoing circuit. If the two circuits have the same number of coils, currents and voltages in both wires will be identical. But if there are more coils in your outgoing wire, then the charge induced there will have decreased current and increased voltage, making it ideal for long-distance transmission. If there are fewer, you’ll decrease your voltage and increase your current, making your electricity ready for local use. Voltage is directly proportional to the number of coils, so a 3:1 ratio of coils in and out will produce an outgoing current at one-third the voltage as incoming.

To get the angles for the remaining hours, use the following formula, where l is your latitude and h is your hour: angle = tan-1(sin l × tan h)

Modern thermometers use mercury—which expands dramatically with heat, boils at a distant 357°C, and doesn’t freeze until 38 degrees below zero—but

Alcohol (see Section 10.2.5) expands more linearly and freezes way down at -173°C, but it boils at a mere 78°C, which is less convenient.

To make actual soap, you’ll need potash, soda ash, or lye: these are alkalines you can produce easily with Appendix C. An alkaline is a substance that at the atomic level accepts protons from any chemical donor: they’re the opposite of acids, which are substances that donate them.* A neat thing happens when you combine alkalines with oils or fats: you induce a chemical reaction called “saponification.” During saponification, the fats chemically combine with the alkalines to form new molecules: long and skinny hydrocarbon chains.* These chains have a cool (and for you, very useful) property: one end loves water and hates oil, while the other end hates water and loves oil.*

The easiest soaps are made with potash and soda ash (see Appendices C.5 and C.6, respectively): just mix them in a pot of boiling fat. Use the fat and grease from whatever animals you’re eating, but don’t forget to purify them first in a simple but stinky process called “rendering.” Take your collected fats and grease, chop them up, put them in a pot, add an equal amount of water, and boil. The fats will melt into the water: once they’re all melted away, add more water (about the same amount as the first time), and let your pot cool overnight. The fats will rise to the top of the water—we’re using the fact that oil and water don’t mix to our advantage here—and the impurities will sink to the bottom. That top layer of purified fats is what you’re interested in. Scoop that off, put it in a new pot, bring it to a boil again, and add in your potash or soda ash. Stir until it’s well mixed, which can actually take several hours. Now you’ve got two options: you can let it cool, which produces a soft, jelly-like brown soap, or you can throw some salt in and then let it cool. This causes little pieces of soap to solidify out of the liquid and congeal on top, which will give you a harder, more pure soap that’s also easier to store. You can optionally purify your hard soap even further by boiling it in water and doing that salt trick again to precipitate it out.

best soaps with lye instead of potash or soda ash. Lye is more strongly basic, so it makes more effective soaps. It can be tricky to know when you’ve got lye in the right concentration, but historically soap makers have used the test of “will an egg or a potato float in it” as a rough metric for the proper concentration. Add more water to a lye to weaken it, and boil it down to strengthen

Tanning transforms these skins into leather: a substance so resistant to rot

Immediately after slaughtering the animals, lay the skins flat and cover the fleshy side in salt or sand, which will dry them out and delay decomposition. In a few days the hides will become hard and almost crispy, and they can then be transported to your tanning area. Once there, you’ll soak the hides: this cleans off dirt and gore and softens them up again. Scour the skins to remove any remaining flesh, then soak them in urine—this loosens the hair, which can then be scraped off. You’ll make the poop slurry we advertised earlier by mixing poo and water,* and then soak your skins in that: enzymes in the poop will cause the skins to ferment, softening them and making them more flexible. You can help this process by standing in your poop slurry and kneading the skins with your feet—just keep telling yourself you’re crushing grapes—but be sure to wash up with soap and water afterward, or better yet use nonhuman power (like a waterwheel) to knead the skins for you. After all this, two things will have happened: your animal skins will be soft, flexible, and ready for tanning, and nobody will want to get anywhere near you. To tan these skins, you’ll need to collect some appropriately named “tannins,” which come from trees containing the equally appropriately named “tannic acid.” The bark from oak, chestnut, hemlock, and mangrove trees is high in tannin, as is the wood of cedar trees, redwood trees, and more. Tannins are brown, so if you’re using wood instead of bark, look for r...

To get wool ready for spinning, first clean it in soapy water to remove any grease, then comb it. Combing aligns your wool fibers in the same direction, while also breaking up any clumps and puffing it up into a fluffy ball that’s ready to be spun.*

The flyer is a simple U-shaped piece of wood that can rotate freely around the bobbin, with hooks on its wings so you can adjust the point on the bobbin that the thread is wound around. As the bobbin rotates and pulls wool in, it forces the flyer to rotate too, at exactly the same speed. All you need to do is change the speed of the flyer: you can do this by adding a brake to it (a belt around the flyer’s shaft can be tightened or loosened to adjust its tension), or by adding a separate drive belt to the flyer, spinning it at a different rate. When the flyer and bobbin no longer rotate at identical speeds, a twist is introduced to your wool as it’s spun.

Once you have two lengths of thread, you can twist them together to form a stronger twine, using the exact same wheel. Just twist them in the opposite direction those threads were spun in, and they’ll naturally lock together.

acacia plants produce lactic acid, which is spermicidal.

It’s called “silphium” and it grows naturally along the coast of what’s now Libya. You’re looking for something with a thick stalk, a rounded head of flowers at the top, and distinctive heart-shaped fruit pods.

The ideal building has three elements: it is sturdy, useful, and beautiful.

By following the instructions in Appendices C.3 and C.4, you can convert limestone into quicklime, and quicklime into slaked lime—which reacts with carbon dioxide in the air to harden on its own. Add some clay (or sand and water) to your slaked lime, and you’ve just invented mortar: an easily spreadable paste that dries like stone. Replace some of that sand and water with straw or horsehair to increase its tensile strength and you’ve invented plaster: a substance durable enough to be used for exterior coverings that is also waterproof once it’s cured. This makes plaster a great way to build underground food storage:

But all these technologies require air and time to fully cure: plaster can take months! The solution is to add aluminum silicates to your mortar. This creates hydraulic cement: a mortar that not only cures faster and is water resistant but can also cure underwater

Cement’s great, but you can make it even better simply by mixing gravel, stones, or rubble into it. That’s concrete!

Iron is the sixth most abundant element in the universe and the fourth most common element in the Earth’s crust,

When I told my father I was going to be an actor, he said, “Fine, but study welding just in case.”

The challenge is when metals reach this point, their surfaces tend to oxidize, which prevents a good weld. By sprinkling sand (or ammonium chloride, or saltpeter, or a mixture of all three; see Appendix C) on top of your metal,

One large tree can be transformed into upward of 15,000 sheets of paper,

You can let them soak in water for a few days to get the fibers loosened, before grinding or beating your plant fibers down into, well, a pulp. To speed this process up you can add sodium bicarbonate or sodium hydroxide (see Appendices C.6 and C.8, respectively) to water and simmer your wood chips or rags in there, which chemically separates the plant fibers.

drag a mesh screen up through it—you can make it with either metal or threads (see Section 10.8.4)—which will collect some of the fibers in a flat layer. Flip your screen upside down to remove the pulp, press it to remove the water and force the fibers together, and let it dry. You just made paper!

One cannot discover new lands without consenting to lose sight, for a very long time, of the shore.

dilute sulfuric acid reacts with iron to produce hydrogen gas.* Dilute sulfuric acid by (slowly) adding it to 3⅓ times its weight in water, put iron filings in a barrel, and pour your diluted acid on top of the iron filings in a 2:1 ratio by weight—meaning 2kg of acid gets poured on top of 1kg of iron. This will react to give you your hydrogen! You can then pass it through a second barrel filled with slaked lime (which you can make in Appendix C.4) to remove any acid carried over with the gas, which you’ll want to do because otherwise the gas you’re producing could eat through your balloon: historically, rarely a good thing. The sulfuric acid will exhaust itself before the iron does, so you can drain out the used-up acid from the first barrel and refill it with more until there’s no more iron left to react. Your hydrogen production apparatus will look like this:

Around 400kg of iron and 800kg of acid will produce about 140 cubic meters of hydrogen, and 10 cubic meters of hydrogen is enough to lift around 10.7kg, depending on the day’s air pressure, temperature, and humidity.

There are fifteen valid logical syllogistic structures you can produce, and we’re going to save your civilization years of hard-core logic and philosophizing by giving them to you right now: Major premise Minor premise Conclusion All M are P All S are M Therefore, all S are P No M is P All S are M Therefore, no S is P All M are P Some S are M Therefore, some S are P No M is P Some S are M Therefore, some S are not P All P are M No S is M Therefore, no S is P No P is M All S are M Therefore, no S is P All P are M Some S are not M Therefore, some S are not P No P is M Some S are M Therefore, some S are not P All M are P Some M are S Therefore, some S are P Some M are P All M are S Therefore, some S are P Some M are not P All M are S Therefore, some S are not P No M is P Some M are S Therefore, some S are not P All P are M No M is S Therefore, no S is P Some P are M All M are S Therefore, some S are P No P is M Some M are S Therefore, some S are not P Table 16: Valid logical syllogisms. This is something that took humanity thousands and thousands of years to puzzle out, and it all fits in a single 15×3 grid! Hooray!

The color purple’s association with royalty also originates in purple pigments being extremely expensive:

natural ammonium chloride salts (NH4Cl) from the ground—they form naturally from volcanic gases, so you can find these white crystals growing near volcanic vents.