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

by Ryan North

cooler water makes bread that takes longer to rise, and water that’s too hot—around 60°C—will kill your yeastie beasties.

If you want vinegar, just take your beer (or any sugary and unpasteurized liquid) and leave it to ferment some more.

The vast majority of plants on the planet are killed by salt, and only 2 percent of all plant species can tolerate high salinity.*

Salt is used as the iodine delivery vector for two reasons: it doesn’t go bad, and people tend to eat a predictable amount—nobody,

Iodized salt is one of the simplest and cheapest public health measures humans have ever come up with, and it enhances both physical health and intelligence at the same time:

Many birds have a high metabolism and breathe rapidly, so they succumb to carbon monoxide and other toxic gases before humans do. Specifically, canaries faint in the presence of carbon monoxide about twenty minutes before humans.

You can distinguish dry clay from rocks by scratching it: if your scratch easily brings away a fine powder, that’s dry clay, and some water will fix that right up!

With kilns—which are really just specialized ovens—you unlock not just better pottery but also glassware, metalworking, and more:

that clay that you first cooked in your campfire has given you access not only to better kilns but also to molten metals and the ability to shape them! It’s brought you from the Stone Age, through the Bronze Age, and all the way into the Iron Age,

Outward-curved lenses (called “convex lenses”) are easier to make than concave lenses—since blowing a glass sphere produces convex shapes by default—so you’ll find farsightedness (not being able to see close things clearly) initially easier to correct than nearsightedness.

Eyeglasses were first invented in the 1200s CE in India and brought to Europe through Italy.

However, it took five hundred years—well into the 1700s CE—before anyone suggested that glasses might be conveniently held in place by arms that use our ears as anchors.

You’re looking for a mixture of about 60 to 75 percent silica,* 5 to 12 percent quicklime, and 12 to 18 percent soda.

Attach a crank to your waterwheel and you’ve changed its rotational motion into a back-and-forth one, which you can use to invent mechanical saws, pumps, or bellows. Replace your crank with a trip hammer and your waterwheel can now repeatedly smash rocks (or hammer steel) instead.

streams and waterfalls that were too small for waterwheels will power a Pelton turbine just fine.

If your pistons power a flywheel instead of your machinery directly, the wheel will continue to rotate even when the pistons aren’t providing power, generating a much smoother force.

This is why a steel flywheel is safer than a cast-iron one: steel’s greater strength minimizes the chance any flywheel inside your machinery transforms itself into a surprise metal bomb.

You can increase the energy any flywheel stores by increasing either its size or its speed.

mastery of electromagnetism will allow your civilization to expand beyond riversides and mines to conquer the continent, the planet, and eventually time itself.

The core mechanic is incredibly simple: get something to rotate, wrap that rotating thing in coils of wire, put a magnet in the middle, and you’ll generate electricity.

If you think of electricity like water, then your wires are pipes, current is the amount of water moving through those pipes, and voltage is the pressure driving the water along.

just as batteries could’ve been invented at any point in history once basic metals were discovered, so too could’ve power plants and transformers.

Modern wristwatches use tiny pieces of quartz to keep time: it’s the second-most abundant mineral on Earth, and it has a useful property called “piezoelectricity.”

In eccentric orbits, planets don’t always orbit at the same speed: rather, they speed up as they orbit close to the sun, and slow down as they orbit farther away.

These were thermo-scopes (a way to see temperature), rather than thermo-meters (a way to measure it).

Alternatively, wine—a delicious mixture of water and alcohol—has been used to mitigate the effects of alcohol’s low boiling point and water’s weirdness.

An alkali 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.

Tanning transforms these skins into leather: a substance so resistant to rot that leather shoes from 3500 BCE have survived into the modern era.

hardwoods generally contain more tannin than softwoods.

wrapping limbs in too-tight rawhide has been used for torture.

If you consider the goal of health care to be giving another person more years of life than they’d otherwise have, then just helping premature babies survive is the most effective and efficient health care you can provide.

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,

you can add animal blood too, which will produce tiny bubbles in the cement that make it more resistant to the stresses of freeze-thaw cycles.

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

It was only when an obscure Roman manuscript from 30 BCE (written by the architect and engineer Vitruvius, whose quotation graces this section) was rediscovered in a Swiss library in 1414 CE that the secrets of cement and concrete were recovered.

only alloys with carbon levels between 0.2 percent and 2.1 percent get the “steel” label.

Kitchen knives—that can hold a tough edge and won’t break easily—have around 0.75 percent carbon.

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

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

You can print with either wood or clay letters, but you can also use them as prototypes for new metal type by pressing the letters into either fine sand or a soft metal (copper works well), and then pouring liquid metal into that impression. Printers eventually settled on a standard metal to forge type with: an alloy of lead, tin, and antimony called “type metal” that produces strong, long-lasting letters.

Oil-based inks better adhere to metal type, and they don’t soak into paper as deeply, which prevents words from becoming blurry.

The printing press will allow your civilization, and the people within it, to become their best selves: entertained, educated, informed, and up-to-date,

(pneumatic tires helped bicycles lose their early nickname of “boneshakers”),

bikes have also been fundamental to early women’s liberation.

radiation—which is just energy moving through space—that

A diode is a device that lets electrical current flow in only one direction.

itself. A skilled sailor with a proper boat can achieve a travel speed of 1.5 times the wind.

If you draw a line between when humans had the technological prerequisites (fire and the drop spindle needed for fabric creation) and the time when they finally took flight for the first time, that line covers almost ten thousand years.

dilute sulfuric acid reacts with iron to produce hydrogen gas.*

the first manned heavier-than-air powered flight was in 1874 CE with a steam-powered aircraft and predated the Wright brothers by almost thirty years.*