Tang dynasty
The inventor Ding Huan (fl. 180 AD) of the Han dynasty invented a rotary fan for air conditioning, with seven wheels 3 m (10 ft) in diameter and manually powered. In 747, Emperor Xuanzong had a "Cool Hall" built in the imperial palace, which the "Tang Yulin" () describes as having water-powered fan wheels for air conditioning as well as rising jet streams of water from fountains. During the subsequent Song dynasty, written sources mentioned the air conditioning rotary fan as even more widely used.
William Symington
William Symington quickly saw a way to marry the efficiency of the Watt engine with the simplicity of that devised by Thomas Newcomen. Encouraged by Gilbert Meason, Symington demonstrated the practicality of his idea and his improved atmospheric engine was patented in 1787. When Watt sent someone to make a sketch of how this new engine worked, he discovered that the steam was condensed under a second piston and this was then pushed down when fresh steam entered the cylinder, forcing out the condensate. The power piston worked by the atmospheric pressure acting on the vacuum created by the condensing steam.