The Knowledge: How to Rebuild Our World From Scratch (27 page)

Persuading nitrogen gas to combine with hydrogen for ammonia is just the first step, though. Once the nitrogen has been fixed, you’ll want to convert it to a more generally useful chemical: nitric acid. The ammonia is oxidized in a high-temperature converter—not just a furnace, but a vessel that essentially burns the ammonia gas itself as a fuel, using a platinum-rhodium catalyst. This is actually the same alloy as in the catalytic converter stuck in the exhaust pipe of cars to reduce pollution emissions, and so should be relatively easy to scavenge in the aftermath. The nitrogen dioxide produced is then absorbed into water to create nitric acid.

Neither of these products—ammonia or nitric acid—can be poured directly onto a farmer’s field to help boost crop growth: the first is too alkaline, the second too acidic. But if you simply mix the two together, they neutralize and form the salt ammonium nitrate, and this makes a fantastic fertilizer, as it packs a double dose of accessible nitrogen. As we saw in Chapter 7, ammonium nitrate is also useful in medicine, as it decomposes to release the anesthetic nitrous oxide. It is a powerful oxidizing agent, too, and so can be used to make explosives.
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So for a post-apocalyptic society maturing into an industrialized civilization, the Haber-Bosch process will liberate you from dependence on collecting animal manure or bird guano, soaking timber ashes, or digging saltpeter mineral deposits for your vital nitrate supply, and instead enable you to mine the virtually limitless reservoir of nitrogen in the atmosphere.

Today, the Haber-Bosch process pumps out around a hundred million tons of synthetic ammonia every year, and fertilizer made from it sustains one-third of the world’s population—around 2.3 billion
hungry mouths are fed by this chemical reaction. And since the raw materials in the food we eat become assimilated into our cells, about half of the protein in our bodies is made from nitrogen fixed artificially by the technological capability of our own species. In a way, we’re partially industrially manufactured.

TIME AND PLACE

Men go and come, but earth abides.

E
CCLESIASTES
1:4

The ideas ruins evoke in me are grand. Everything comes to nothing, everything perishes, everything passes, only the world remains, only time endures.

D
ENIS
D
IDEROT,
Salon of 1767

IN THE LAST CHAPTER
we built up to some pretty complex industrial chemistry, suitable for supporting the requirements of a burgeoning post-apocalyptic society generations into its recovery after the Fall. Now I want to go right back to basics. What could survivors do to work out from absolute scratch the answers to two crucial questions: “What time is it?” and “Where am I?” This is far from a frivolous exercise: being able to trace your passage through time and through space are critical capabilities. The first allows you to measure the passing of time during the day and to track the days and seasons, a prerequisite for successful agriculture. We’ll see what observations you can make to reconstruct the calendar surprisingly accurately, and, if you wanted to, even work out far in the unknown future what year it is, the classic question that falls from the hero’s lips in every time-travel film. The second is important for allowing you to trace your location around the globe in the absence of recognizable landmarks. This is crucial for
working out where you are in relation to where you want to be, and enables you to navigate for trade or exploration.

Let’s look at time first.

One of the most fundamental functions of any civilization is to be able to track your passage through the seasons, to know the best moments to sow and then harvest and so prepare for the inescapable approach of the deadly winter or dry season. And as a society becomes more sophisticated and its routines more rigorously structured, telling time within the day becomes increasingly important. Clocks are indispensable for regulating the duration of different activities and synchronizing civic life. Everything from the working hours of tradesmen to the start and end of market, and in religious societies the moment to congregate at the place of worship, is choreographed to the beat of the hour.

In principle, you can meter time by capitalizing on any process that proceeds at a constant rate. A plethora of different methods have been used historically, and will be useful in the early stages of a reboot if no clocks survived. These include the regular dripping of a water clock, with time indicated as a graduated line down the side of either the reservoir or the receptacle; or the trickle of sand or other granular material through a small hole; or the remaining level in an oil lamp; or a scale marked down the side of a tall candle.

The water clock and hourglass work on similar principles of gravity, but unlike the pressure forcing liquid out the bottom of the water clock, the rate of flow of the hourglass is largely independent of the height of the remaining sand column, and this superior timer became common from the fourteenth century on. But while an hourglass can measure duration, it can’t itself tell you the time of day (without a
rigorous system of repeatedly inverting timers from the moment of dawn). So how can you determine from first principles what the time is?

The structure of our hectic modern lives is dictated today by our wall clocks and daily planners, but these are both no more than formalizations of the primordial rhythms of the planet we live on. On the timescale of our everyday experience, the natural rhythms of the Earth play out too slowly for most of us to be aware of more than the regular beat of day and night or the more gradual cycling of the seasons. If we were able to twist a dial and accelerate the passage of time around us, these planetary periodicities would become much more apparent. (The descriptions below are for a point of view in the northern hemisphere, but if you’re in the south the principles are the same.)

With the Sun sliding more rapidly through the sky, shadows swing across the ground, pivoting around the base of the objects casting them. As the Sun races to the west and slips out of view after a cruelly abbreviated sunset, the sky drains color to indigo and the pitch darkness of nighttime descends. The vast spattering of stars across the heavens are not the static points you are used to, but thin lines of light wheeling around the dome of the firmament. They trace out concentric rings nestled within one another, and right in the center, the north celestial pole, no movement is discernible. In the very bull’s-eye of this pattern there happens to lie a star, Polaris, or the North Star, around which all others appear to whirl, before the firmament lightens again with dawn.

Next, you notice that the fiery streak of the Sun’s trajectory across the sky isn’t steady over the weeks, but that the arc rocks gently back and forth. During summer the Sun arcs the highest, providing long, warm days, but during winter it’s almost as if the Sun is taking a shortcut, at more northerly latitudes barely hauling itself above the horizon before soon sinking out of view again. The highest and lowest reach of this rocking, where the solar arc seems to slow and stop before swinging back in the opposite direction, is called the solstice (from the Latin
for the Sun standing still). The winter solstice (coincident with the summer solstice in the southern hemisphere) is the shortest day of the year, and corresponds to the Sun rising from its southernmost point on the horizon. Ancient astronomical sites like Stonehenge have monuments aligned to the location of sunrise on these special days.
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So how can you use these natural rhythms and cycles to determine the time?

To a first approximation, the Sun’s journey across the sky as the world spins,
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and by extension the shifting location of shadows, indicates the time of day. Anyone who has ever tried to stay in the shade of a tree or a beach umbrella will be acutely aware of how it shifts. So if you plant a stick upright in the ground, the rotation of its shadow will indicate the passing of time. This is, of course, the essence of a sundial. The time when the shadow is shortest is midday, or noon. For the most accurate results, the stick (gnomon) should be angled directly toward celestial north, indicated by the polestar, as we saw earlier.

If you can fashion a hemispherical shell to sit around the base of the stick, or a circular arc, the hour lines are simply marked out at regular intervals, as it allows for a direct projection of the celestial sphere onto the curved surface of the sundial. A flat circular sundial is much easier to actually construct, but the marking of the hour lines is more involved because the shadow will move more slowly around noon than in
the morning or evening. You can divide the day into as many hours as you like. Our convention of breaking down a full day into two halves of twelve hours each originates with the Babylonians (possibly linked to the twelve signs of the zodiac: the band of constellations that the Sun and planets appear to move through in their trajectory across the sky).

The major revolution in timekeeping in our history, though, and a technology you’ll want to aim toward during recovery, is that of a mechanical “clockwork” clock.
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This is a marvelous contraption that ticks with a rhythmical beat like a heart. Four key components are needed for this action: a power source, an oscillator, a controller, and the clockwork gearing.

The primary part of any mechanism is the power source, and the simplest means for providing this is a weight suspended on a string wrapped around a shaft, so that it turns as the weight descends under gravity. But the crucial problem is how to regulate the release of that stored energy to drive the slow movements of clockwork rather than letting the weight simply drop straight to the ground.

The beating heart of the mechanical clock, the bit that provides the regular timing signals, is called the oscillator. The ideal low-tech solution is a simple pendulum: a swinging mass on a rigid rod. The physical principle you’re exploiting is that the period of a pendulum—the time it takes to swing down through a small angle and return to its initial position—is determined by its length. A pendulum will swing with exactly the same beat even as friction and air drag gradually reduce the amplitude of its swing, and it is this incredible regularity that makes it such a useful component for a clock. The third element, the controller, performs the vital job of integrating the timing signal from the
oscillator to regulate the power source. The pendulum escapement is a jagged-toothed gearwheel that repeatedly locks and disengages with a two-armed lever that rocks with the pendulum swing. At the top of each swing, the released escapement jolts around one step from the pull of the drive weight, and its angled teeth give a little nudge to keep the pendulum going. So this ingenious arrangement captures the regular impulse of the swinging bob to trickle out the stored energy one tick at a time. The twin demands for a nice long pendulum and high drop for the drive weight dictate the design of many timepieces to look like tall grandfather clocks.

THE KEY COMPONENTS OF A MECHANICAL CLOCK. THE DROP OF THE WEIGHT (BOTTOM LEFT) DRIVES THE GEAR CHAIN, WITH THE ESCAPEMENT (TOP) RELEASING THE TRAPPED WHEEL TO TURN ONE TOOTH AT A TIME AS IT ROCKS BACK AND FORTH. THE ESCAPEMENT IS COUPLED TO THE REGULAR BEAT OF A PENDULUM (NOT SHOWN).

After this, it’s a relatively simple affair to design a system of gears that essentially performs a mathematical calculation to adjust the stepwise turn of the escapement to a driven wheel that turns a full circle every 12 hours for the hour hand of a clock face, and a minute hand geared to this at a ratio of 60:1. It is another legacy of the ancient Babylonians that we chop hours into 60 minutes (the name deriving from the Latin
partes minutiae primae
, meaning first small part) and those further into 60 seconds (Latin
partes minutiae secundae
). Pendulum clocks
also enable the precise measuring of natural processes and experiments, a development that in our history contributed enormously to the tool kit of investigators through the scientific revolution.
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The length of hours indicated by the roving shadow of a sundial varies over the year: a winter hour is shorter than a summer hour. Only on two days of the year are the solar hours all equal: the equinoxes (meaning literally “equal night” because day and night are both 12 hours long).
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These special days occur in spring and autumn, and if you’re standing on the equator at noontime the Sun passes directly overhead and your shadow disappears beneath your feet. The morning of either equinox is easy to spot anywhere in the world, as the Sun rises due east (at right angles to the celestial pole you observed). It is this standard equinoctal hour (which can be captured from a sundial by an hourglass for comparison later) that mechanical clocks are set to count. Sundials display what is known as apparent solar time, which can deviate by as much as 16 minutes from the mean solar time kept by mechanical clocks with their fixed equinoctial hour. With the proliferation of mechanical clocks came a potential source of confusion, however—which of the two time systems do you mean: the uniform hour of machinery, or solar time, counting the number of hours since sunrise? Thus from the fourteenth century on it became necessary to specify a time as an hour “of the clock,” such as “three
o’clock.”

Indeed, there’s an even deeper historical link between the modern clock face hanging on your wall and ancient sundial technology. Mechanical clocks displaying the time by an hour hand twirling around a
dial were designed to be intuitively understood by people accustomed to reading the shadow line of a sundial. They first appeared in medieval European cities, and in the northern hemisphere the shadow from a sundial gnomon always rotates the same way: the direction we therefore adopted as “clockwise” for the hour hand. If during the reboot a mechanically advanced southern civilization reinvents the clock, the hands might instead turn in the direction we would consider anticlockwise.

So much for keeping time during the day. What can you do, working from the very basics, to track longer cycles of time—feeling the pulse of the seasons and reconstructing a calendar?