Editing Odometer (section)

=== Imperial China ===
[[File:Han dynasty odometer cart.jpg|thumb|right|A [[Han dynasty]] stone rubbing of a horse-drawn odometer cart]]

==== Han dynasty and Three Kingdoms period ====
The odometer was also independently invented in [[History of Science and Technology in China|ancient China]],{{sfn | Needham | 1965 | pp=280–286}} possibly by the prolific inventor and early scientist [[Zhang Heng]] (78 AD – 139 AD) of the [[Han dynasty]]. By the 3rd century (during the [[Three Kingdoms]] Period), the Chinese had termed the device as the 'jì lĭ gŭ chē' (記里鼓車), or '[[li (unit)|li]]-recording drum carriage' (Note: the modern measurement of li = {{Cvt|1640|ft|order=flip}}).{{sfn | Needham | 1965 | p=281}} Chinese texts of the 3rd century tell of the mechanical carriage's functions, and as one li is traversed, a mechanical-driven wooden figure strikes a drum, and when ten li is traversed, another wooden figure would strike a gong or a bell with its mechanical-operated arm.{{sfn | Needham | 1965 | p=281}}

Despite its association with Zhang Heng or even the later [[Ma Jun (mechanical engineer)|Ma Jun]] (c. 200–265), there is evidence to suggest that the invention of the odometer was a gradual process in Han dynasty China that centered around the ''huang men'' court people (i.e. eunuchs, palace officials, attendants and familiars, actors, acrobats, etc.) that would follow the musical procession of the royal 'drum-chariot'.{{sfn | Needham | 1965 | p=283}} The historian [[Joseph Needham]] asserts that it is no surprise this social group would have been responsible for such a device, since there is already other evidence of their craftsmanship with mechanical toys to delight the emperor and the court. There is speculation that some time in the 1st century BC (during the Western Han dynasty), the beating of drums and gongs were mechanically-driven by working automatically off the rotation of the road-wheels.{{sfn | Needham | 1965 | p=283}} This might have actually been the design of one [[Luoxia Hong]] ({{circa|110&nbsp;BC}}), yet by 125 AD the mechanical odometer carriage in China was already known (depicted in a mural of the [[Xiaotang Mountain Han Shrine|Xiaotangshan Tomb]]).{{sfn | Needham | 1965 | p=283}}

The odometer was used also in subsequent periods of Chinese history. In the historical text of the ''[[Book of Jin|Jin Shu]]'' (635 AD), the oldest part of the compiled text, the book known as the ''Cui Bao'' ({{circa|300&nbsp;AD}}), recorded the use of the odometer, providing description (attributing it to the Western Han era, from 202 BC–9 AD).{{sfn | Needham | 1965 | p=282}} The passage in the ''Jin Shu'' expanded upon this, explaining that it took a similar form to the mechanical device of the [[south-pointing chariot]] invented by [[Ma Jun (mechanical engineer)|Ma Jun]] (200–265, see also [[differential (mechanical device)|differential]] gear). As recorded in the ''[[History of Song (Yuan dynasty)|Song Shi]]'' of the [[Song dynasty]] (960–1279 AD), the odometer and south-pointing chariot were combined into one wheeled device by engineers of the 9th century, 11th century, and 12th century. The ''[[Sunzi Suanjing]]'' (Master Sun's Mathematical Manual), dated from the 3rd century to 5th century, presented a mathematical problem for students involving the odometer. It involved a given distance between two cities, the small distance needed for one rotation of the carriage's wheel, and the posed question of how many rotations the wheels would have in all if the carriage was to travel between point A and B.{{sfn | Needham | 1965 | p=282}}

==== Song dynasty ====
The historical text of the ''[[History of Song (Yuan dynasty)|Song Shi]]'' (1345 AD), recording the people and events of the Chinese [[Song dynasty]] (960–1279), also mentioned the odometer used in that period. However, unlike written sources of earlier periods, it provided a much more thoroughly detailed description of the device that harkens back to its ancient form ([[Wade-Giles]] spelling):

<blockquote>
The odometer. [The mile-measuring carriage] is painted red, with pictures of flowers and birds on the four sides, and constructed in two storeys, handsomely adorned with carvings. At the completion of every li, the wooden figure of a man in the lower storey strikes a drum; at the completion of every ten li, the wooden figure in the upper storey strikes a bell. The carriage-pole ends in a phoenix-head, and the carriage is drawn by four horses. The escort was formerly of 18 men, but in the 4th year of the Yung-Hsi reign-period (987 AD) [[Emperor Taizong of Song|the emperor Thai Tsung]] increased it to 30. In the 5th year of the Thien-Sheng reign-period (1027 AD) the Chief Chamberlain Lu Tao-lung presented specifications for the construction of odometers as follows:{{sfn | Needham | 1965 | p=283}}
</blockquote>

What follows is a long dissertation made by the Chief Chamberlain Lu Daolong on the ranging measurements and sizes of wheels and gears, along with a concluding description at the end of how the device ultimately functions:

<blockquote>
The vehicle should have a single pole and two wheels. On the body are two storeys, each containing a carved wooden figure holding a drumstick. The road-wheels are each 6 ft in diameter, and 18 ft in circumference, one evolution covering 3 paces. According to ancient standards the pace was equal to 6 ft and 300 paces to a li; but now the li is reckoned as 360 paces of 5 ft each.{{sfn | Needham | 1965 | p=283}}
</blockquote>

[Note: the measurement of the Chinese-mile unit, the li, was changed over time, as the li in Song times differed from the length of a li in Han times.]

<blockquote>
The vehicle wheel (li lun) is attached to the left road-wheel; it has a diameter of 1.38 ft with a circumference of 4.14 ft, and has 18 cogs (chhih) 2.3 inches apart. There is also a lower horizontal wheel (hsia phing lun), of diameter 4.14 ft and circumference 12.42 ft, with 54 cogs, the same distance apart as those on the vertical wheel (2.3 inches). (This engages with the former.){{sfn | Needham | 1965 | p=283}}
</blockquote>

<blockquote>
Upon a vertical shaft turning with this wheel, there is fixed a bronze "turning-like-the-wind wheel" (hsuan feng lun) which has (only) 3 cogs, the distance between these being 1.2 inches. (This turns the following one.) In the middle is a horizontal wheel, 4 ft in diameter, and 12 ft circumference, with 100 cogs, the distance between these cogs being the same as on the "turning-like-the-wind wheel" (1.2 inches).{{sfn | Needham | 1965 | p=284}}
</blockquote>

<blockquote>
Next, there is fixed (on the same shaft) a small horizontal wheel (hsiao phing lun) 3.3 inches in diameter and 1 ft in circumference, having 10 cogs 1.5 inches apart. (Engaging with this) there is an upper horizontal wheel (shang phing lun) having a diameter of 3.3 ft and a circumference of 10 ft, with 100 cogs, the same distance apart as those of the small horizontal wheel (1.5 inches).{{sfn | Needham | 1965 | p=284}}
</blockquote>

<blockquote>
When the middle horizontal wheel has made 1 revolution, the carriage will have gone 1 li and the wooden figure in the lower story will strike the drum. When the upper horizontal wheel has made 1 revolution, the carriage will have gone 10 li and the figure in the upper storey will strike the bell. The number of wheels used, great and small, is 8 inches in all, with a total of 285 teeth. Thus the motion is transmitted as if by the links of a chain, the "dog-teeth" mutually engaging with each other, so that by due revolution everything comes back to its original starting point (ti hsiang kou so, chhuan ya hsiang chih, chou erh fu shih).{{sfn | Needham | 1965 | p=284}}
</blockquote>