Evidence of Han-era mechanical engineering comes largely from the choice observational writings of sometimes disinterested Confucian scholars. Professional artisan-engineers (jiang 匠) did not leave behind detailed records of their work. Han scholars, who often had little or no expertise in mechanical engineering, sometimes provided insufficient information on the various technologies they described. Nevertheless, some Han literary sources provide crucial information. For example, in 15 BC the philosopher Yang Xiong described the invention of the belt drive for a quilling machine, which was of great importance to early textile manufacturing. The inventions of the artisan-engineer Ding Huan (丁緩) are mentioned in the Miscellaneous Notes on the Western Capital. Around 180 AD, Ding created a manually operated rotary fan used for air conditioning within palace buildings. Ding also used gimbals as pivotal supports for one of his incense burners and invented the world's first known zoetrope lamp.