The mule-Jenny was an intermittent wool spinner that made yarn of the strands coming from the carder.
It worked intermittently, spinning in two stages: it first stretched and twisted the yarn and then, after a pause, it rolled the wool onto the spindle.
It is a semi-mechanised machine, because part of its operation was completely manual. An operator must constantly monitor it because if a strand broke, the process had to be stopped in order to prevent it from spoiling the rest.