An article by J. G. Martindale of the Scottish Woollen Technical College explaining how carded wool slivers are spun into woollen yarn on the spinning mule. It covers the roles of twist and drafting, the balance between fibre slippage and grip, and the mule's sequence of movements: delivery, drafting, final twisting, jacking in, backing off, and winding on to form the cop. It also compares mule spinning with ring spinning and gives British production figures for the early 1950s. Illustrated with photographs, a cross-section of the mule, cop-forming diagrams and twist graphs.