I'd have to ask you to open it to be sure, but it looks to me to be a transformer in a porcelain casing. Most likely to operate a low voltage bell or chime.
You are all right, a small transformer used primarily for low voltage transfer. Up here in the sticks I've seen many in the cellars that were used for telephone lines. Most were white, blue being seen the least. Neat converstion piece, I saved a few.
Mark
Thanks everyone for the replies. I found it in a basement of a real old abandoned house, just laying on the floor. I think it was probably ripped out and left after the copper thieves did their thing in that basement.