Being the proud () owner of a home built in 1886, I have had to repair many broken sash cords or in a couple of instances chains where they were repaired sometime between then and today. Over the weekend we were working on a 3rd floor window which was constructed differently than the others in the house.
The window is a small two piece double sash on each piece. Routine stuff. It also has a third single piece 4 pane hinged window which opens inward. The total window area is about 2' x 4'.
The sides of the frame have the typical channel cut for the wooden separator/divider slat to rest and keep the top window in place. The unusual thing is that the bottom window has no trim to keep it in place. This would be the necessary result of having the 3rd window. The 3rd window would not swing closed with any lower window molding.

In trying to figure out why the 3rd window and the difference in channeling from the other windows in the house, the only reason I can come up with is that the concept was to be able to remove both hung windows in warmer months and double the air flow. Then close the hinged window when it rained.

The other side of the house has an identical window, almost directly opposite the one we just repaired. The only difference is that window is asided a staircase and at a height level so unreachable that it is totally impractical to think of opening and closing it routinely. I can't remember it ever being opened. The windows face south and north. The prevailing wind in summer is S/SE. The south side window is fortunately the working window.

So, I am left thinking that the design was to permit the double hung windows to be removed in warmer weather for increased air flow straight across the third floor to keep the entire house cooler. Any old house owners have any ideas?

And another curiosity: Why would the 1886 contract call for Florida pine floor boards for the first floor and VA pine for the second and third floors ??? That one beats the heck out of me? IS FL pine harder?