These insulators were installed upon the upper exterior walls of Boston's underground subway, completed in 1897. In this photo are four CD 140 "Jumbo" insulators per crossarm that were in active service. This line ran along and through the northerly side of Boylston station, starting at the end of Park station and ending just before Arlington station. The "crossarms" were spaced about 12 feet apart and the length of this line was at least a quarter of a mile. The insulators used are long gone but the pins and arms are still there. Click "Previous" for a close view of the insulators.