That’s a picture from a probe, looking at the structure under a stair in an Upper East Side rowhouse-turned-apartment-house. The photo was taken on an angle – you try sticking your phone in a hole and shooting blind and see how you do – so the piece of wood that occupies most of the upper half of the picture is a stair stringer, running on an angle from horizontal with the stair to support the treads. The pipe is a sprinkler, put in for the multiple-dwelling conversion. The bottom of the photo is the top of the ceiling below the stair, angled with the stair until it flattens for the hallway on the left.
The thing about this photograph that is interesting beyond my specific reason for taking it (which was to see the connection of the stronger to the trimmer at the top of the stair) is that set of parallel lines on the side of the wood. They’re marks from the sawmill and they tell a story.
For a very, very long time, people have been turning round (or roundish) tree trunks into rectangular beams. If the beam is about the same size as the log, you can simply use axes and adzes, but if the beam is smaller (something like cutting a 3×10 out of a 16-inch diameter tree), then saws are the way to go. This is ancient technology, replacing the even older method of splitting a log. Sawmills are also very old, with some recorded in Roman times. The sawmills in medieval times and after look a lot like modern mills in broad terms: the logs are moved forward into a powered saw. How the logs move has changed, as has the source of power and the type of saw.
In this case, the straight lines tell us that the saw was a straight up-and-down saw rather than a circular saw. It was probably a ganged saw, with several parallel blades simultaneously cutting several pieces out of a log. The marks are at a regular spacing because the cradle holding the log was being advanced by a ratchet, rather than one of the constant-movement methods such as a conveyor belt. (For most people, this is where they picture “The Perils of Pauline” or one of the endless re-uses of the trope, with the heroine tied to a log in a sawmill, heading for a big circular saw.)
The house was built in 1888, which is pretty late in the nineteenth century for an up-and-down sawmill with a ratcheted conveyor. Maybe the wood sat in a yard somewhere for a decade or two, but more likely it was simply a mill that had not yet modernized. It means nothing for our work at this building, but the details always tell a story.
