Barn Ornament

Down in Somerset County, next Saturday, the John Henry Mellot auction company will be holding an estate auction at a local farm.

Since they posted a photo of this round object mounted decoratively at the gable of the barn, I expect it will probably be for sale.

I’m not actually looking to own one of these myself, but I am curious as to what is the identity of this large, obviously antique, article of agricultural technology?