Slowly shaking its fist above Daniel’s head is an arm made of giant, knot-ridden timbers joined by iron hasps that must have been sledge-hammered out in a forge somewhere nearby. Depending from its end is a gargantuan chain, its links about the size of a grown man’s femur, joined together by hand-forged cotter pins as big as bears’ claws. In Newcomen’s mind, Daniel knows, these links are meant to be of uniform size. In practice each is a little different, the differences averaging out as the chain disappears over the horizon of the curving arch-head that terminates the great arm. From it depends the piston, which fills a vertical cylinder the size of a mine-shaft. Packed round the piston’s edge to form a seal is a matted O of old rope yarn, called junk, clamped down by a junk ring, secured with rustic nuts. Plenty of steam leaks out around it, but most stays where it belongs. The opposite end of the arm is linked to a pump rod consisting of several tree-trunks squared off and bound together with iron bands, plunging into the earth and pulling on giant sucking and splurging equipment too deep down for Daniel to see. Compared to all of this, the brains of the thing are tiny, and easy to miss: a man, on a platform a storey or two below where Daniel is standing, surrounded by pushrods, bell-cranks, and levers and supplying information to the machine when needed, which is not very frequently. At the moment, he is supplying information to Orney and Saturn, who have joined him down there.