 How to bring into existence many of the things proved theoretically in mathematics, where the worth of the device consists of removing hindrances that, perhaps, hindered their existence. There are numerical devices—like the algebra, geometrical ones—like those for measuring the surface of bodies which are impossible to access, astronomical devices, optical—like the art of mirrors— musical, and mechanical. (Alwuzad 1988: 253. 7–11; IB-taaliq: 28. 9–11)