An International Correspondence Schools-style instruction paper (Section 37) on spinning woolen yarn on the self-acting mule. It begins with the history of spinning and the quality of roving, then describes the mule's headstock and carriage and each of its mechanisms in detail: delivery rolls and roving stop-motion, draft scroll and dwell motion, rim band and accelerated speed, easing-up, backing-off, drawing-in, quadrant, and builder motion. It closes with the sequence of operation, bobbin clips, spindle bands, waste, power requirements and review questions. Illustrated with many numbered mechanical line drawings.