controller. Donald Routledge Hill wrote the following on the automatic controls underlying the mechanical trick devices described in the book: The Banu Musa also developed an early fail-safe system for use in their trick devices, as described by Hill: Automatic crank The non-manual crank appears in several of the hydraulic devices described by the Banū Mūsā brothers in their Book of Ingenious Devices. These automatically operated cranks appear in several devices, two of which contain an action which approximates to that of a crankshaft, anticipating Al-Jazari's invention by several centuries and its first appearance in Europe by over five centuries. However, the automatic crank described by the Banu Musa would not have allowed a full rotation, but only a small modification was required to convert it to a crankshaft. Valves A mechanism developed by the Banu Musa, of particular importance for future developments, was the conical valve, which was used in a variety of different applications. This includes using conical valves as "in-line" components in flow systems, which was the first known use of conical valves as automatic controllers. Some of the other valves they described include: Plug valve Float valve Tap Other mechanisms The double-concentric siphon and the funnel with bent end for pouring in different liquids, neither of which appear in any earlier Greek works, were also original inventions by the Banu Musa brothers. Some of the other mechanisms they described include a float chamber and an early differential pressure sensor. Machines and devices Automatic fountains The book describes the construction of various automatic fountains, an aspect that was largely neglected in earlier Greek treatises on technology. In one of these fountains, the "water issues from the fountainhead in the shape of a shield, or like a lily-of-the-valley," i.e. "the shapes are discharged alternately—either a sheet of water concave downwards, or a spray." Another fountain "discharges a shield or a single jet," while a variation of this features double-action alternation, i.e. has two fountainheads, with one discharging a single jet and the other a shield, and the two alternating repeatedly. Another variation features one main fountainhead and two or more subsidiary ones, such that when the main one ejects a single jet, the subsidiaries eject shields, with the two alternating. The Banu Musa brothers also described the earliest known wind-powered fountain, which is described as, "operated by wind or water, it discharges a single jet or a lily-of-the-valley."