I think you've got the answer. Here is a drawing of a device that looks like it has most of the elements of the one you've shown. Note there are three leveling screws in the photo you posted, two short rusty ones and one bright shiny one with a locking bolt in the middle. These would serve the same function as the level adjusters in the drawing below. The two wires in your photo could come from the thermopile inside the glass globe like the drawing shows. Thermoelectric pyranometer.