You wrote: ‘Yes, it's interesting of course, but it doesn’t involve a mention of any physical action or appearance.’
The Zhuangzi passage refers to something physical. It refers to the self-leveling property of water, and to how the master carpenter (da jiang) uses that property as his standard. From what I can gather, Chinese carpentry levels were of two types. One consisted of a vertical piece attached to a horizontal base. At the top of the perpendicular post was attached a plumb line. When the surface on which the base rested was level, the plumb line would be perfectly aligned with the vertical post. Another type had a trough or groove in the cross-beam that was filled with water, with a float at each end of the groove.
There is a book by Klaas Ruitenbeek, _Carpentry and Building in Late Imperial China_ (Brill, 1996). It’s a very expensive book, but some of the content is accessibly via Google Books, here: http://books.google.com/books?id=KH2XJVKxgIMC&dq=early+chinese+carpentry&pg=PP1&ots=1VsUyaB8CT&source=in&sig=LCZ86kJrcOIQpHUgU95Z2dobaFI&hl=en&sa=X&oi=book_result&resnum=12&ct=resu
The book quotes a description of the use of the water level in an 1850 source:
“To level a platform, low walls must be piled up at the four corners, and a three-foot long pole must be driven into the ground in the middle. It should have a small tenon at the top. On this, a wooden trough about two feet long is fitted, in such a way that it can be turned freely toward all four corners. It is about two inches wide, and can be filled with water. At both ends, a ‘wooden duck’ is made to float. This is what is called a water-level.
One worker is standing at a corner, holding a foot-rule and a brush. Another worker stands next to the level, leaning on a stick and looks with one eye over the floats. When he turns his hand downward, the other worker lowers the rule he is holding; when he turns his hand upwards the other worker moves the rule up. When the rule is level with the floats, he waves his hand. The worker holding the rule then makes a mark on the wall with his brush. After the three other corners have been treated the same way, the platform can be made level.”
Ruitenbeek also describes how the plumb-line type of level was used:
“Suppose that, on a building site, point A is lower than B, C, and D. At A, a wooden pole is driven into the ground in such a way that its upper end remains slightly higher than B, C, and D. At b, a few feet further on, a second pole is driven into the ground. The level is laid over these two poles. If the plumb-line hangs straight along the centre line of the upright post of the instrument, the ends of the poles are on a level plane. In the same way, the poles at b and c are compared, and so on.” (Ruitenbeek, pp. 45-47)
These are descriptions from modern sources, but from what I can gather, the features of both types of carpentry levels were typical of the types used at the time of Zhuangzi.
What is pertinent to our Taijiquan Lun discussion is that both types of carpentry tools share some of the same properties and characteristics that operate in balance scales and in steelyards.
It’s interesting that you would refer to Zhuangzi’s writings as “pure philosophical ideas.” My view of Zhuangzi is entirely different from that!