World house...?

When James Longstreet and D.H. Hill took over Henry Piper's house prior to the battle of Antietam, they told the Pipers to leave because of the impending battle. Piper and his family ended up at his brother Daniel's place along the Potomac.

Until recently, no photograph was known to exist of that place. I have found one and, of course, it will be in my upcoming book. (Have I mentioned I'm writing a book?) Anyway, it has an interesting inscription. It starts with "World house on the Piper farm where I was cared for when sick..." Does anyone know what that means? I googled it and found MLK made a speech about this, but I am talking 1889.

I spent the afternoon today looking around for the site of the house and I think I have found it. I scouted it out from the canal about a year ago but only today had time to drive up and introduce myself to the owner. It is a horse farm surrounded by private property so I wanted to be careful.

So, anybody know what a "World house" is?