The universal joint in antiquity

[Eleatic Guest]

I've come across another use of the universal joint or Cardan joint in ancient technology! Purists will say that this mechanism, like the other two I quickly return to, is no true universal joint, but this is actually how Jenemann, an absolute expert in the study of ancient scales, repeatedly refers to the device. Ok, let's settle on the term "variant of an universal joint". :mrgreen:

So, Jenemann cites half a dozen examples of Roman steelyards, chiefly from Switzerland (4) and Germany (2), where the pan is suspended by a tilt-and-swivel mechanism IMO identical to the one used in Roman ballistae. The function of the universal joint is two-fold: the tilting mechanism smoothes out oscillations of the steelyard, thus enhancing its sensitivity, while the swivel mechanism allows the balance beam to be rotated around its own axis, so that it can suspended on another hook (which changes the lever ratio and thus the weighing range).

The main discussion is in Jenemann, Hans, Zur Geschichte der Waagen mit variablem Armlängenverhältnis im Altertum, Trierer Zeitschrift, Vol. 52, 1989, 319-352 (339f., 344, 347 + fig. 8, 9, 14)

The other two applications, in Roman single boom cranes and Greek and Roman ballistae, are pointed out by Duncan here: Roman cranes

Since the universal joint holds a high prestige for mechanical ingenuity, I think this sheds more positive light on the general level of Roman technology, in particular since this steelyard technique, is mainly found in outlying provinces where you would not easily expect such refinement.

[Eleatic Guest]

Found a fourth application and the artifact is still intact. It is this fire hose! According to Oleson, Greek and Roman mechanical water-lifting devices: the history of a technology, 1984, p. 269, who calls the mechanism "a type of universal joint", the Y-shaped nozzle of the force pump can be directed to any direction (the Y-shaped end up and down, and the main vertical shaft around its own axis).

Makes four.

[Epictetus]

Forgive the semi-personal question, but have you ever considered writing an article on ancient technology? (Or have you already done so?) You seem to have a knack of finding things like this that shake up the conventional wisdom of ancient technology.

[Eleatic Guest]

You don't need not to apologize, it is no personal question. I have been thinking about this for a while, but the field is vast and for every question I find an answer to two new ones arise....the Socrates paradoxy...the more you objectively know, the less you feel you know for certain...kind of common trap for many writers I think, but an article shouldn't be impossible, although I would have no idea where to turn to for publishing it. Hm, I need thinking about this.