5 of the Greatest and Most Mysterious Mechanical Computers

Who needs transistors when you've got gears?
John Loeffler

Usually when we think of computers, we probably imagine glowing displays, interconnected networks sharing digital information, and more software applications than anyone one person could ever come close to using — but that's only part of computing's story.

Analog computers, and later mechanical computers, were an integral part of humanity's pursuit of scientific discovery, fueled by our desire to anticipate future events and outcomes. For a species that conquered the entire world thanks to our larger brains and toolmaking prowess, it's no surprise that we've been using artificial tools to augment and enhance our intelligence as far back as our history goes — and probably even longer than that.

From the careful positioning of stones in England, to the soaring water clocks of China's Song Dynasty to the precise arrangement of mechanical gears in the visionary inventions of Blaise Pascal and Charles Babbage, analog and mechanical computers have served our forebearers well and helped them not just survive but thrive by transcending the bounds of our biology.

Stonehenge Calculates the Solistice

5 of the Greatest and Most Mysterious Mechanical Computers
Source: garethwiscombe/Wikimedia Commons

In Salisbury Plain in the south of England, a collection of about 100 massive and roughly even-cut stones form a pair of standing rings whose purpose is lost to history, but whose construction began before the invention of the wheel and took at least 1,500 years to complete, and possibly even longer.

The work of several distinct cultures and built up in phases over millennia, Stonehenge is one of humanity's most enigmatic monuments. Well into the Middle Ages, Stonehenge was thought by some to be the handiwork of Merlin's sorcery, while later archaeologists attributed its construction to mystical Celtic druids — it predates the arrival of the Celts in England by at least 1,000 years, however.

Whoever constructed it (or contributed to its construction at some point) clearly understood the significance of the winter solstice in the northern hemisphere. The winter solstice marks the shortest day of the year and the longest night, but rather than a gloomy occasion, the winter solstice is typically celebrated by many cultures as the great turning point of their annual routine.

If today is the longest night of the year, then tomorrow is when the gloom and cold of winter begin to recede, eventually giving way to spring and summer. The winter solstice is typically considered an occasion for hope and optimism, and the stones of what would have been the tallest trilithon at Stonehenge when they were still standing would have perfectly framed the setting sun on the winter solstice, marking this important seasonal turn.

During the summer solstice, meanwhile, the sun rises directly behind a single large stone lying just outside of Stonehenge known as the Heel Stone and shines its first rays of light directly into the heart of the monument. As the longest day of the year, many cultures around the world throughout history have marked the summer solstice with feasts and festivals to various sun gods and harvest deities, and the prehistoric peoples around Stonehenge likely did the same.

While we might not see something like Stonehenge as a computer, on a very basic level, that's what it is, even if its purpose is very narrowly defined by modern standards.

The position of the sun throughout the year, relative to the trilithon stones of Stonehenge's two rings are equivalent to digital bits in a processor: either the sun rises or sets between a specific trilithon or it does not: either true or false, 1 or 0. When you see a 1, you know that a solstice has come; otherwise 0, and you know you have to wait until tomorrow to run this crude calculation again.

While it seems like overkill to spend millennia constructing an analog computer with dozens of massive stones weighing 40 tons that stand two stories tall and sourced from up to 200 miles away just to tell you if today is one of two very specific days out of the year, it still counts.

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So congrats, prehistoric peoples of England, all that hard work from multiple cultures and many thousands of people paid off in the end.

The Antikythera Mechanism Charts the Heavens

5 of the Greatest and Most Mysterious Mechanical Computers
Source: Joyofmuseums/Wikimedia Commons

Without question, the ancients were really into astrology.

The motion of the moon, planets, and stars across the night sky and the complicated zodiacs that various civilizations developed to make sense of the many patterns they saw influenced everything from government administration to religious practices and observances.

The foundations of modern astronomy were laid by some of the oldest human structures ever found, like Göbekli Tepe in Turkey, which may have been one of the earliest observatories ever built when it was constructed around 12,000 years ago.

We didn't just build observatories though, we built computers to help us make sense of the cosmos. That's at least what researchers say the incredible Antikythera mechanism, considered by most to be the oldest-known mechanical computer, was designed to do.

Discovered in 1901 in an ancient shipwreck off the coast of the Greek island Antikythera, the Antikythera mechanism is believed to be more than 2,000 years old. Greek scientists have dated the device as being constructed sometime between 205 BCE at the earliest and around 87 BCE at the lastest, and it was already a well-used device when the ship carrying it sank sometime between 70 and 60 BCE.

Originally constructed in a wooden box containing an intricate array of at least 37 bronze gears — if the recovered inscriptions on the device are correct — the Antikythera mechanism represented a mechanical model of the then-known universe (basically the inner solar system along with Jupiter and Saturn).

By setting a couple of dials on the front and turning a crank on the side of the box (which has long since decayed), you could advance through the Egyptian calendar and the 12 signs of the zodiac to predict what you would see in the night sky at a given date in the future. It might even have told you the date of the next ancient Greek Olympic games.

Scientists also don't believe that this device was unique for the time. The intricacy of the gear setup and the model of the universe it predicted probably evolved from simpler mechanical computers with more narrowly defined predictions, meaning that such devices might have been in use even earlier than the second century BCE.

To really drive the point home, it would take more than a millennium for a device as sophisticated as the Antikythera mechanism to be re-created elsewhere in the world, showing us how easily technological progress can be rolled back, and just how advanced Hellenistic science really was.

The Castle Clock: Ismail al-Jazari 'Ingenious Mechanical Device'

Ismail al-Jazari was a 12th-century inventor, scholar, mechanical engineer, and mathematician. He was famous for his extraordinary work developing mechanical devices towards the end of the Islamic Golden Age, which stretches from the 8th century to 1258, when Ghengis Khan sacked the Abbasid caliphate's capital of Baghdad in modern-day Iraq.

Born in the upper Mesopotamian region of Jazira, not much is known about al-Jazira beyond what he wrote about himself in his Book of Knowledge of Ingenious Mechanical Devices, but we do know that he was the court engineer for a vassal dynasty of the caliphate in eastern Anatolia, a position he inherited from his father.

Ismail al-Jazari is often known as the father of robotics for his brilliant mechanical automata and complex waterclock devices that would often feature animals and people performing prescribed actions like beating a drum to sound the time.

Possibly his greatest was the Castle Water Clock. While water clocks have been in use since the ancient Greeks, going as far back as the third century BCE, and some of the most advanced water clocks of medieval China and the Islamic world were magnificent works of engineering, clockwork isn't the same thing as computing generally.

We say generally because not only was al-Jazari's Castle Water Clock a masterpiece of mechanical engineering, its intricate, coordinated action and its ability to be "reprogrammed" by adjusting the water level of the driving mechanism in measured intervals to adjust for the length of the day throughout the year earns it the distinction as the world's first programmable analog computer.

Blaise Pascal's Pascaline Does the Math for the Masses — Kinda

5 of the Greatest and Most Mysterious Mechanical Computers
Source: David.Monniaux/Wikimedia Commons

Blaise Pascal is widely regarded as one of the great polymaths of the Scientific Revolution, formulating theories about everything from mathematical probability to atmospheric science. He also made a major contribution to the field of computing with his Pascaline, widely considered the world's first practical mechanical arithmetic calculator.

In 1639, Pascal's father was appointed to a regional tax administration position in the French city of Rouen. He didn't need to do any particularly onerous mathematics like calculating the orbit of a comet or planetary bodies, he just needed to keep track of the typical account, balance, and payment figures that any accountant would have to deal with.

At the time, there was no easy way to ease the monotony of repeated simple arithmetic like addition, subtraction, multiplication, and division without resorting to cumbersome reams of mathematical tables with precalculated figures for various operations.

This inspired Pascal to develop a machine that could add and subtract mechanically using wheels and switches (multiplication and division could also be accomplished by using a series of additions and subtractions). However, unlike previous attempts at mechanical calculators, the carry function between 9 and 0 from one wheel to the next wheel was entirely automated.

This allowed a user to simply input the numbers and the operation they wanted to perform and the calculation would automatically cascade the values from one wheel to the next. This, along with other mechanical improvements, allowed Pascal to shrink his Pascaline to a functional size so that it could be used in an office environment.

While this is a milestone development in the history of business machines, as such devices would be known in the modern era, more important for the field of computation is that Pascal developed a mechanical solution to automating the carry function in a machine performing arithmetic.

Yes, this definitely doesn't sound like a huge deal, but this innovation is critical to the operation of a modern computer's CPU. The digital-equivalent process to the Pascaline's mechanical automatic carry functions is what allows a CPU to function at such incredible speeds. So, in a very real sense, the Pascaline is the analog-equivalent to an arithmetic processing unit, one of the modern computer processor's most foundational components.

Babbage's Analytical Engine Uses Steam Power to Transcend the Calculator

If the mechanical and analog devices we've covered so far were the launchpad for computing, then the Analytical Engine was the rocket, though it has yet to ever be built.

In 1822, the English mathematician Charles Babbage completed the first iteration of what would become his most famous invention, the Difference Engine.

It was a mechanically-driven machine used for computing large tables of numbers via a mathematical technique called the finite difference method — hence the name — which uses only arithmetic addition to calculate figures (this eliminated the need to implement the mechanically far more complicated division and multiplication operations in the device).

After introducing his invention in a paper that year at the Royal Astronomical Society, the Difference Engine caught the attention of the British government, which was very interested in a way to quickly and cheaply produce mathematical tables used for government administration. They did have a sprawling empire to administer, after all.

The government gave Babbage nearly £18,000, or about $2 million in modern US dollars, over a 20 year period, to develop the machine before eventually giving up on the effort in 1842, largely because the more Babbage worked on the Difference Engine, the bigger the project became.

By 1834, Babbage had given up on building a workable Difference Engine (much to the government's annoyance) after envisioning a machine that was far more advanced than simply calculating and tabulating the results of polynomial equations. This new Analytical Engine would consume Babbage's focus for the rest of his life.

5 of the Greatest and Most Mysterious Mechanical Computers
A woodcut taken from Charles Babbage's original design drawing for a section of his Difference Engine No. 1, left, and a closeup of a replica Difference Engine built from Babbage's design, housed at the London Science Museum, right | Source: Wikimedia CommonsCarsten Ullrich/Wikimedia Commons

Much like his earlier Difference Engine, the Analytical Engine featured hundreds of columns of numbered wheels and gears that would hold a decimal number up to 40 digits long.

Turning so many individual gears and wheels was impossible with a hand crank like previous mechanical calculators that had done, so Babbage's Difference Engine and Analytical Engine would both be powered by steam engines to drive the delicate mathematical calculations through the series of interlocking gears.

And while the Difference Engine calculated differential functions, the Analytical Engine could calculate anything that was calculable. Using punched cards as input — inspired by those used to feed design patterns into the Jacquard loom — and which could output results on a mechanical printer as well as punched cards — which could then be read into the Analytical Engine again — the Analytical Engine was an early forerunner of the early ENIAC and UNIVAC punch card computers of the mid 20th century.

There was also a store of internal memory capable of holding 1,000 separate 40 decimal digits.

In a modern computer, a single decimal digit can be represented in binary numbers with ln(10)/ln(2), or roughly 3.3219 bits, which multiplied by 40,000 decimal digits total gives us about 132,878 bits, or 16.6 kilobytes of internal memory.

Most important of all, the Analytical Engine was capable of being programmed through punchcards to perform conditional branching and looped operations on the data in its memory to produce new figures, which could then be stored in memory again and used to decide data-manipulation rules and grammars.

In this manner, the actual mathematical operations the machine could carry out were not internally defined by any of its gears or wheels, but by the input itself. 

This is what scientists call a Turing-complete language like the assembly language used by modern processors to run everything from your smartphone to the world's fastest supercomputers or the early BASIC language that spawned a generation of computer programmers in the 1960s.

On a conceptual level, the Analytical Engine is no different than your laptop computer, other than the fact that it would have been several meters long and three meters tall when fully constructed.

5 of the Greatest and Most Mysterious Mechanical Computers
Lady Ada Lovelace, whose algorithm for computing Bernoulli numbers on Babbage's Analytical Engine is the first documented computer program ever written | Source: Wikimedia Commons

Lady Ada Lovelace, the daughter of famed poet Lord Byron, was a trailblazing mathematician and friend of Babbage's, who saw the potential for his Analytical Engine and wrote copious notes on its workings in the margins of journal articles describing its design.

She described how the machine, which hadn't yet been built and never would be, could be programmed to calculate a sequence of Bernoulli numbers, which cemented her place in history as the world's first computer programmer, as well as providing the first proof of concept for Babbage's Analytical Engine.

Babbage died in 1871 before he was able to complete his work, and even though leading scientists and mathematicians of the era saw the revolutionary brilliance of his Analytical Engine, they believed that such a machine could never actually be built, or at least that it would be so expensive to build as to render its construction impossible.

It would be another 65 after Babbage's death before another computer science pioneer, Alan Turing, would build on Babbage's Analytical Engine and herald in our modern Computer Age.

But for all of our electric power, many billions of transistors on a single silicon chip, and interconnected networks that make up the internet, there is still the allure of this greatest mechanical computer of all, the Industrial Revolution's lingering What-If.

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