Analogue Computers - Antikythera Mechanism

[OneHungLow]

While reading up on the Apollo Guidance Computer (AGC) I was interested to read about the use of analogue computers such as the sophisticated Beckman analogue computer used to aid flight and navigation simulation with the digital computers in order to mimic the dynamic conditions approaching those found in a space environment.

https://www.ibiblio.org/apollo/hrst/archive/1722.pdf

The sophistication of the analogue computers used in the Apollo programme (with its Greek divinity) brought to mind the amazing story of the ancient Antikythera Mechanism which was a very sophisticated Ancient Greek hand-powered orrery, described as the oldest known example of an analogue computer used to predict astronomical positions and eclipses decades in advance.

[OneHungLow]

Analogue Computers...

These are examples of analog computers that have been constructed or practically used:

Boeing B-29 Superfortress Central Fire Control System

Deltar
E6B flight computer
Kerrison Predictor
Leonardo Torres y Quevedo's Analogue Calculating Machines based on "fusee sans fin"
Librascope, aircraft weight and balance computer
Mechanical computer
Mechanical integrators, for example, the planimeter
Nomogram
Norden bombsight
Rangekeeper, and related fire control computers
Scanimate
Torpedo Data Computer
Torquetum
Water integrator
MONIAC, economic modelling
Ishiguro Storm Surge Computer

https://www.nasa.gov/centers/dryden/mul ... -6910.html

[Karearea]

The Antikythera mechanism: consider the centuries of observation and the elegant civilisation required to devise and create such an instrument.

Fascinating documentary - thank you for posting.

[Boac]

I don't know about the Antikythera, but it is amazing that some of these ancient astronomical instruments not only worked but were based on the idea that everything revolved around the earth - and still worked??

[Fox3WheresMyBanana]

Epicycles, BOAC.
Wheels within wheels.
Adding motion around a smaller circle, with a centre point in motion around a larger circle, works to describe the motion as seen from Earth.
It's a very nasty bit of mathematics in cartesian co-ordinates, but easy in vector maths, and quite straightforward to build into a mechanism.

epicycles1-1079401791.jpeg (3.62 KiB) Viewed 1539 times

Prior to the discovery of gravity, it was thought that bodies would move in accordance with the will of the Heavens/Gods.
The circle being a perfect shape, it seemed entirely appropriate that the motions of heavenly objects could be described with a simple combination of two of them.

[Boac]

I'm with the science, but find it amazing that the 'predictions' all worked when the science was wrong!


.........or was it..............?

[Fox3WheresMyBanana]

Many ways to skin a cat.
It's a basic problem with science - just because it works doesn't mean it's right.
And also an advantage - most of the models that are taught in school science* are 'wrong', but they work to a sufficient degree of accuracy for all situations the average person will encounter, and are simple to teach and remember.

*So are some in RAF ground school.

[OneHungLow]

Many ways to skin a cat.
It's a basic problem with science - just because it works doesn't mean it's right.model
And also an advantage - most of the models that are taught in school science* are 'wrong', but they work to a sufficient degree of accuracy for all situations the average person will encounter, and are simple to teach and remember.

*So are some in RAF ground school.

Good point. For example I was taught about atoms using the Thomson atomic model, and then told that it had been supplanted by the Rutherford model, only then to be told by our science teacher that this had been supplanted by the Bohr model, which in turn was quickly demolished in my matriculation year by Herr Schrodinger's model. Many still think of an atom as consisting of a heavy nucleus in a microscopic universe with solid ball like electrons circling the nucleus just like those models made of balls and sticks in the science lab, an inaccurate model which however still suffices in many cases even today, when in fact we are dealing with a shadowy indeterminate world of wave like probabilities that may manifest as point like particles whose position and velocity cannot be simultaneously measured, and whose reality may be nothing more than perturbations in a number of all pervading fields, such as the Higgs field, that have no corporeal manifestation in the classical world save for their effect, e.g. mass in the case of the Higgs field and its eponymous particle!

A model, or simulation as in the case of the ingenious Antikythera device is merely a simulation that may also give valuable practical empirical predictive readings, e.g. the position of the moon in the night sky on a particular date and time, without imparting any deep information about the underlying orbital model, which was often profoundly wrong in many cases, particularly in the medieval world. That been said, it is clear that many of the ancient Greek polymaths clearly knew that the world was not flat, vide. Eratosthenes (he of the famous sieve) who clearly knew the world was basically circular, when he measured the world's circumference (by definition) and I suspect that many Greeks also knew very well that the earth was not the centre of the solar system, and that much ancient knowledge was lost or suppressed until the dead hand of medieval religion, which persecuted empirical scholars such as Galileo, Giordano Bruno (who was burned at the stake for his pains) and Copernicus who sought to overturn the heliocentric view of the world, was thrown off.

Talking of epicycles, and the fantastic ingenuity of those who sought to simulate or model the solar system and/or universe while retaining elements of the Ptolemaic geocentric model, it is always enlightening to see the efforts of even prodigiously intelligent astronomers like Tycho Brahe, who sought to replace Copernicus's heliocentric system with a hybrid of the Ptolemaic geocentric system: by a geo-heliocentric system. It took a deal of great effort and intellect to be palpably wrong it seems.