Vitruvius

“ With my best efforts I have striven to set forth an obscure subject clearly in writing, but the theory of it is not easy, nor readily understood by all, save only those who have had some practice in things of this kind. If anybody has failed to understand it, he will certainly find, when he comes to know the thing itself, that it is carefully and exquisitely contrived in all respects. ”

“ So, when the keys, touched by the hand, drive the sliders forward and draw them back regularly, alternately stopping and opening the holes, they produce resonant sounds in a great variety of melodies conforming to the laws of music. ”

“ So, when the levers are raised, the elbows draw down the bottoms of the cylinders as far as they can go; and the dolphins, which are mounted on joints, let the cymbals fall into the cylinders, thus filling the interiors with air. ”