Hard to tell for certain from the photo what the thing sticking out from the centre of the rotating arm is, BUT if conceiveably it could be a cutting tool, this could be a ball turning attachment for a round bed lathe like the Drummond:
Drummond Lathes
The clamp would hold the attachment on the bed with the 'tool' at approximately centre height, and the handle would rotate the tool in an arc whose radius is set by the tool projection. It doesn't matter in which plane the tool turns relative to the stock, it will describe a circle that will form a hemispere on the end of the work
AWEM