picked up this Shibe park (Phila A's stadium) postcard. Its dated Sep 1 1913, and the writer talks about a game - Nats vs A's - and "Johnson" hitting a HR. According to baseball-reference, it was WoJo's 8th of the 24 he hit in his career and it came off of A's pitcher "Boardwalk" Brown.
http://www.baseball-reference.com/pl...=johnswa01&t=b