Engraving depicting Colvins hydraulic milking machine: corrugated rubber suction cups were placed over the teats. Oscillating pumps gave the motion of a calf sucking; and created a partial vacuum; and the milk was drawn off into churns set in the floor. At the right of the picture the cow is being released from the stall; and the cups have been removed and swung out of the way and can be seen by the churn. Dated 19th Century.