with seven wheels that measured 3 m (10 ft) in diameter; in the 8th century, during the Tang Dynasty (618–907), the Chinese applied hydraulic power to rotate the fan wheels for air conditioning, while the rotary fan became even more common during the Song Dynasty (960–1279). The first rotary fan used in Europe was for mine ventilation during the 16th century, as illustrated by German mineralogist and metallurgist Georg Agricola (1494–1555). Rudder, stern-mounted and vertical axial: Lawrence V. Mott, who defines a steering oar as a rudder, states the ancient Egyptian use of stern-mounted rudders can be traced back to the 6th dynasty (2350–2200 BC). Mott states that the method of attachment for rudders in the Arab, Chinese, and European worlds differed from each other, leading him to doubt the spread of the Chinese system of attachment by socket-and-jaws or block and tackle (versus European pintle-and-gudgeon invented by c. 1180 AD). In regards to Mott's definition of a steering oar as a rudder, Joseph Needham, Richard Lefebvre des Noëttes, K.S. Tom, Chung Chee Kit, S.A.M. Adshead, Paul Johnstone and Sean McGrail state that a steering oar is not a rudder; the steering oar has the capacity to interfere with handling of the sails (limiting any potential for long ocean-going voyages) while it was fit more for small vessels on narrow, rapid-water transport; the rudder did not disturb the handling of the sails, took less energy to operate by its helmsman, was better fit for larger vessels on ocean-going travel, and first appeared in China. Leo Block writes of the use of the steering oar in the ancient Mediterranean world (specifically in regards to the Phoenicians, 1550–300 BC): "A single sail tends to turn a vessel in an upwind or downwind direction, and rudder action is required to steer a straight course. A steering oar was used at this time because the rudder had not yet been invented. With a single sail, a frequent movement of the steering oar was required to steer a straight course; this slowed down the vessel because a steering oar (or rudder) course correction acts like a break." The oldest depicted rudders at the back of a ship, without the use of oars or a steering oar, comes from several ceramic models of Chinese ships made during both the Western and Eastern eras of the Han Dynasty (202 BC – 220 AD). According to the scholars