From the Sung Shih,
compiled in 1345 from sources many years older:
In the 5th year of the Thien-Shêng reign-period of the emperor Jen
Tsung (+1027), Yen Su, a Divisional Director
in the Ministry of Works, made a south-pointing carriage. He memorialized
the throne, saying, [after the usual historical introduction]:
Throughout the Five Dynasties and until the reigning dynasty there
has been, so far as I know, no one who has been able to construct such
a vehicle. But now I have invented a design myself and have succeeded in
The method involves using a carriage with a single pole (for two
horses). Above the outside framework of the body of the carriage let there
be a cover in two storeys. Set a wooden image of a hsien (immortal) at
the top, stretching out its arm to indicate the south. Use 9 wheels, great
and small, with a total of 120 teeth, i. e.
(A) 2 foot-wheels (i.e. road-wheels, on which the
carriage runs) 6 ft. high and 18 ft. in circumference,
(B) attached to the foot-wheels, 2 vertical subordinate
wheels, 2.4 ft. in diameter and 7.2 ft. in circumference, each with 24
teeth, the teeth being at intervals of 3 inches apart,
(E) then below the crossbar at the end of the pole
two small vertical wheels 3 inches in diameter and pierced by an iron axle
(iron axles according to another translator),
(D) to the left 1 small horizontal wheel, 1.2 ft.
in diameter, with 12 teeth, and to the right 1 small horizontal wheel,
1.2 ft. in diameter, with 12 teeth,
(C) in the middle 1 large horizontal wheel, of diameter
4.8 ft. and circumference 14.4 ft., with 48 teeth, the teeth at intervals
of 3 inches apart,
(V) in the middle a vertical shaft piercing the centre
(of the large horizontal wheel) 8 ft. high and 3 inches in diameter; at
the top carrying the wooden figure of the hsien.
When the carriage moves (southward) let the wooden figure point south.
When it turns (and goes) eastwards, the (back end of the) pole is pushed
to the right; the subordinate wheel attached to the right road-wheel will
turn forward 12 teeth, drawing with it the right small horizontal wheel
one revolution (and so) pushing the central large horizontal wheel to revolve
a quarter turn to the left. When it has turned round 12 teeth, the carriage
moves eastwards, and the wooden figure stands crosswise and points south.
If (instead) it turns (and goes) westwards, the (backs end of the) pole
is pushed to the left; the subordinate wheel attached to the left road-wheel
will turn forward with the road-wheel 12 teeth, drawing with it the left
small horizontal wheel one revolution, and pushing the central large horizontal
wheel to revolve a quarter turn to the right. When it has turned round
12 teeth, the carriage moves due west, but the wooden figure stands crosswise
and points south. If one wishes to travel northwards, the turning round,
whether by east or west, is done in the same way.
It was ordered that the method should be handed down to the (appropriate)
officials so that the machine might be made.
In the first year of the Ta-Kuan reign-period (+1107), the Chamberlain Wu
Tê-Jen presented specifications of the south-pointing carriage
and the carriage with the li-recording drum (hodometer). The two vehicles
were made, and were first used that year at the great ceremony of the ancestral
If the carriage turns to the right, it causes the small pulley to the left
of the back end of the pole to let down the left-hand (small horizontal)
wheel. If it turns to the left, it causes the small pulley to the right
of the back end of the pole to let down the right (small horizontal) wheel.
However the carriage moves the hsien and the boys stand crosswise and point
The body of the south-pointing carriage was 11.15 ft. (long), 9.5 ft. wide,
and 10.9 ft. deep.
(A) The carriage wheels were 5.7 ft. in diameter,
the carriage pole 10.5 ft. long, and the carriage body in two storeys,
upper and lower. In the middle was placed a partition. Above there stood
a figure of a hsien holding a rod, on the left and right were tortoises
and cranes, one each on either side, and four figures of boys each holding
In the upper storey there were at the four corners trip-mechanism, and
also 13 horizontal wheels, each 1.85 ft. in diameter, 5.55 ft. in circumference,
with 32 teeth at intervals of 1.8 inches apart. A central shaft, mounted
on the partition, pierced downwards.
(C) In the lower story were 13 wheels. In the middle
was the largest horizontal wheel, 3.8 ft. in diameter, 11.4 ft in circumference,
and having 100 teeth at intervals of 1.25 inches apart.
(D) (On vertical axles) reaching to the top (of the
compartment) left and right, were two small horizontal wheels which could
rise and fall, having an iron weight (attached to) each. Each of these
was 1.1 ft. in diameter and 3.3 ft. in circumference, with 17 teeth, at
intervals of 1.9 inches apart.
(B) Again, to left and right, were attached wheels,
one on each side, in diameter 1.55 ft., in circumference 4.65 ft., and
having 24 teeth, at intervals of 2.1 inches.
(F,G) Left and right, too, were double gear-wheels
(lit. tier-wheels), a pair on either side. Each of the lower component
gears was 2.1 ft. in diameter and 6.3 ft. in circumference, with 32 teeth,
at intervals of 2.1 inches apart. Each of the upper component gears was
1.2 ft. in diameter and 3.6 ft. in circumference, with 32 teeth, at intervals
of 1.1 inches apart.
(H) On (Above according to another translator)
each of the road-wheels of the carriage, left and right, was a vertical
wheel 2.2 ft. in diameter, 6.6 ft. in circumference, with 32 teeth at intervals
of 2.25 inches apart.
(E) Both to left and right at the back end of the
pole there were (The left and right back poles each had according
to another translator) small wheels without teeth (pulleys), from which
hung bamboo cords, and both were tied above the left and right (ends of
the) axle (of the carriage) respectively.
The carriage is harnessed with two red horses, bearing frontlets of
Source: Needham. Joseph: Science and Civilization
in China, Volume 4, Part II, 1965