*Model in the Science Museum in London
By the third century AD at the latest, the Chinese had a fully operational, navigational 'cybernetic machine', using the principles of feedback. It was called the 'south-pointing carriage', but had no connection with a magnetic compass. It was a large carriage, 3.3 metres long, 3.3 metres deep, and 2.75 metres wide, surmounted by a jade statue of an 'immortal''-a sage who had achieved immortality. The figure's arm was raised, pointing ahead, and it always faced towards the south, no matter which way the carriage turned. Even if the road were circular, the jade figure would rotate, keeping the finger pointingin the same direction. How was this possible in the third century AD?
... первый навигационный прибор, работающий по принципу обратной связи. На колеснице была смонтирована фигурка человека, которая независимо от направления движения самой колесницы указывала вытянутой рукой на юг. В этом устройстве не использовался магнитный компас.
Колесница — это двухколёсное транспортное средство, на котором установлена фигурка человека, соединенная с колёсами с помощью дифференциальных передач. Благодаря тщательному подбору размеров колёс, направляющих устройств и передаточных чисел, фигурка на верху колесницы постоянно смотрит в одном направлении, тем самым действуя в качестве немагнитного компаса транспортного средства...http://southpointingchariot.carbonmade.com
UNESCO Courier, Oct, 1988
By the third century AD at the latest, the Chinese had a fully operational, navigational 'cybernetic machine', using the principles of feedback. It was called the 'south-pointing carriage', but had no connection with a magnetic compass. It was a large carriage, 3.3 metres long, 3.3 metres deep, and 2.75 metres wide, surmounted by a jade statue of an 'immortal"-a sage who had achieved immortality. The figure's arm was raised, pointing ahead, and it always faced towards the south, no matter which way the carriage turned. Even if the road were circular, the jade figure would rotate, keeping the finger pointingin the same direction. How was this possible in the third century AD? This machine may have been invented even earlier, indeed, as much as 1,200 years earlier. An official history for 500 AD describe show:
'The south-pointing carriage was first constructed by the Duke of Zhou [beginning of the first millennium BC] as a means of conducting homewards certain envoys who had arrived from a great distance beyond the frontiers. The country was a boundless plain in which people lost their bearings as to east and west, so the Duke caused this vehicle to be made in order that the ambassadors should be able to distinguish north and south.'
If this information is correct, the invention would date from about 1030 BC. But Needham suspects that the word 'carriage" was inserted in this account by scribes, and that what is being described is a "southpointer", that is, a compass.
The next person credited with building a south-pointing carriage is the astronomer and scientist Zhang Heng, about 120 AD, although this is also regarded by Needham as doubtful. The only date which he is prepared to accept with certainty is the middle of the third century AD, with the famous engineer Ma Jun as the builder (and, thus, the inventor). The drawing of a pointing figure of jade, taken from the Universal Encyclopaedia of 1601, was copied from a print of 1341.
If the machine did not use a magnetic compass, how did it work? The answer is that it had a train of differential gears, similar to those in a modern automobile. Perhaps the function of a differential gear should be explained as follows. When a wheeled vehicle is turning a corner the wheels on opposite of the vehicle are clearly going to need to turn at different rates since the near side is travelling a shorter distance than the far side. With a hand-cart or horse-drawn carriage, this may not pose such problems. But when a vehicle has power being applied to the axle to make the wheels turn, how is it possible for one wheel to be permitted to speed up a little, and the other slow down a little, on the same axle? This is made possible only by an ingenious combination of gear wheels and flywheels: the differential gear.
When Needham published his volume on mechanical engineering in 1965, he believed that the Chinese had invented the differential gear, and that it had made its first appearance in this south-pointing carriage. If the first south-pointing carriage were the one attributed to the Duke of Zhou about 1000 BC, then the Chinese would indeed have been the inventors; but we must stay on the side of caution, and assume that the first south-pointing carriage was made in the second or third century AD. In that case, we must credit the Greeks with inventing the differential gear, a fact which became known only in 1975, when Professor Derek Price published his book Gears from the Greeks. In this work Price wrote the definitive account of a Greek differential gear dating from 80 BC, which Price said 'must surely rank as one of the greatest basic mechanical inventions of all time". And although a transmission of this invention from Greece and Rome to China was possible, ltis equally possible that the differential gear was independently re-invented in China for the southpointing carriage.
The precision needed in the construction of the south-pointing carriage almost defies belief. For the outside road wheels alone, Needham points out, J. Coales, in The Historical and Scientific Background of Automation, "has calculated that a difference of only one per cent between the wheel circumferences would lead to a change of direction of the pointing figure of as much as 90 per cent in a distance only fifty times that between the two wheels.' This was because the carriage would veer more and more to one side if one wheel were smaller (relative slip). So that for this south-po'nting carriage, the size of the road wheels had to be accurate to a margin of error far less than one per cent, and a commensurate accuracy in size of gear wheels would have been necessary. This points to engineering of such a high order that we may well be justified in hesitating to apply the words "ancient"primitive" to it !
The south-pointing device was basically a reversal of the use of the differential gear in the modern automobile. Today, such gears are used to apply power to turn the wheels and make the vehicle move. But with the south-pointing carriage, which was pulled by animals, the power was transmitted from the wheels, and applied towards the continual adjusting of the position of the pointing figure. Thus it was the differential gear in the machine which turned the figure so that it always pointed to the south. And it did so just as the differential gear operates today, only in reverse.