Page Eleven

One may also consider the diagram of the calf. Si Nong Refers to the Eastern Han scholar Zheng Zhong (d. 83 CE), who held the office of Minister of Agriculture (Da Si Nong) says that the "thigh" is used to describe the fullness of the spoke, while the "calf" original: 骰 (tou), referring to the lower leg or calf bone describes its tapering. The Record the Kao Gong Ji or Artificers' Record further states: "Divide the length of the spoke into three parts and reduce original: 殺 (sha), meaning to taper or thin out one part." This is because a human thigh is naturally thick, but from the knee downward, it is shaved away and becomes thin; the shape of a wheel spoke is exactly like this.

Of the three parts of the spoke's length:

• The thigh the inner portion closer to the hub consists of two parts that are not reduced.
• The calf the outer portion closer to the rim consists of the one part that is reduced.

However, the circumference reduced is only one-third of the spoke's width where it joins the rim. This reduction occurs only on the outward-facing side of the spoke; it is not a reduction of the entire circumference. This thinned portion on the outside, comprising one-third of the width, is called the geng original: 綆, a technical term for the ridge or "neck" of the spoke where it meets the wheel's rim. The reason it is reduced is to "be humble to the mud" An idiomatic way of saying the tapering prevents mud from sticking to or clogging the wheel assembly.

The Artificers' Record says: "Smooth the geng so that the 'claws' original: 蚤 (zao), referring to the tenons that lock into the outer rim may be straight." It also states: "For a wheel of six feet and six inches, a geng of two-thirds of an inch is what constitutes the 'firmness of the wheel'."

The scholar Zheng Kangcheng The influential commentator Zheng Xuan (127–200 CE) notes that this describes the geng as the measurement by which the spoke's "thigh" extends from the mortise. Furthermore, whenever one calculates the track width original: 徹 (che), the distance between the two wheels, one must always add...