Hero's Computer
I got my first computer back in the year dot when, so it seems, men wore bones in their noses and grass skirts were the latest thing in feminine chic - in other words, about twenty years ago! An impressive beast of a machine that packed more power into its plastic case than NASA had used during the moon landings, it had a massive 32Kb of user programmable memory and ran at a blazing fast 6K per second.
Those were the happy days when, if you could cobble together a game based on bitty graphics and random moves, you could retire to the Bahamas within a couple of months and as for those geniuses who produced a VisiCalc clone, the sky was the limit. The rest of us laboriously typed in listings from computer magazines and marvelled as spirograph patterns appeared on our screens or and lists of a hundred names were sorted into alphabetical order in 20 seconds or less.
One program that every self-respecting computer owner had in his stable was called "Turtle Graphics". Controlled by simple two-letter commands such as FD10 for move forward 10 steps or RT45 for right turn by 45 degrees, the pointer in the middle of the screen - which might be a simple triangle or a chunky representation of a turtle for those who owned high-end machines - left behind it a trail.
Once you were satiated with watching your turtle draw a line step by step, you could then progress to the next stage, which was to program a sequence of such steps. Producing a spirograph pattern was relatively easy, but dedicated individuals progressed to producing real works of art that left the rest of us gasping with amazement.
Lauded as a painless way of teaching children how to program, Turtle Graphics have now gone the way of all flesh and it is years since I saw a copy, so I was intrigued to discover that they owe their origin not to the binary age, but over two thousand years ago to the Alexandrian genius, Hero.
Born around AD 10, Hero was the ancient world's greatest mechanical engineer and inventor, devising a number of ingenious machines as well as mathematical formulae for working out the area of a triangle or finding the square root of a number, an impressive achievement when you remember that Greek maths, like the Romans, used letters for numbers and had no concept of the decimal point.
Among his mechanical inventions was a penny-in-the-slot machine for dispensing holy water - vital for hard-pressed priests at a popular temple - and a device that relied on the expansion of air when heated to mysteriously open and close the doors of the temple. In the secular field he invented a moving theatre of mechanical figures which trundled onto the stage without any human intervention, paused for ten minutes while the figures went through a range of motions to represent some myth with which everyone was familiar, and then trundled off stage again.
The impact of something like this can be seen in the description of Santorini, penned by a Roman author, who remarked that overnight a small island appeared in the centre of the caldera, "emerging from the waters as if moved by machinery!" We today would probably speak of magic, but to the ancients machinery was just as mysterious and possibly even more impressive.
Fortunately Hero was a prolific lecturer in the Alexandrian Museum - the shrine of the Muses - and many of his lecture notes have come down to us. A careful study of these notes, conducted a few years ago by Dr Noel Sharkey, professor of Artificial Intelligence and Robotics at Sheffield University, has revealed the secret of Hero's Theatre - it all worked by string!
The first secret was the controlled power for the theatre, which was a weight suspended from a string. As the weight descended - rather like the weights on a cuckoo clock - the string pulled on things and caused them to move. However without control, the hands on your cuckoo clock would whiz round and Hero's theatre would have shot onto the stage, its figures conducted a frenetic burst of gesticulation and movement and then shot back off again.
The makers of your cuckoo clock have devoted considerable ingenuity in constructing an escapement which controls the speed at which everything turns; Hero used a much simpler method. The weight rested on a tube filled with grain; a small hole in the bottom of the tube released the grain slowly and the weight descended with corresponding slowness.
The real genius, however, lay in what happened at the other end of the string, for it appears that Hero mounted his theatre on a three-wheeled carriage and the string, which split in two, controlled the two back wheels.
It should be obvious that winding the string around the axle of each wheel would mean that as the weight descended the string would be pulled and the wheel would turn. The clever bit came when Hero inserted a peg into the axle: by winding the string around the axle five times he could cause the wheel to be drive forward by five rotations. Then he would loop the string around the peg and wind it around the axle in the opposite direction, causing the wheel to go into reverse!
The final step was to give the string a length of slack, perhaps attached to the axle with a spot of beeswax. The string would unwind, propelling the theatre in one direction, then the slack would be pulled loose and the theatre would remain stationary until the slack was all taken up, and finally the weight would pull the string off the peg and the theatre would trundle back off the stage.
Of course, by varying the way in which the string was wrapped around each axle, you could cause the right hand wheel to stop or even go into reverse while the left-hand wheel was still going forward, thus causing the contrivance to steer to right or left.
In other words, Hero's Theatre was a programmable device in exactly the same way as Turtle Graphics were, and not only that, but its power source was entirely renewable and pollution-free. Not bad going for an ancient Greek!
a tube filled with grain It is interesting to speculate on the source for this idea, for several thousand years before Hero the ancient Egyptians were using cavities filled with sand that was slowly released from the bottom as a means of lowering the enormous stone blocks that made up the lid of pharaoh's sarcophagus or formed the immoveable portcullises that blocked access to the tomb chamber. Return
© Kendall K. Down 2009
