This insulator is both procelain and glass. The base is procelain with what appears to be a layer of tar, a copper ring and glass insulator. There was a wire that ran from the top of the glass insulator portion. Any help would be appreciated. The bottom of the porcelain section is marked Line Materials Corp. Thanks, Ed

Thanks to a fellow ICON member I have the information which I will post for others as well:

That's a low voltage (600V nominal operating range) lightning arrester, made by the Line Materials Co. probably between the 40s and early 60s. A lot of these were used on RR signal lines for protection. Typically the latter circuits ran at 480 volts.