Have you heard of an alidade? I hadn’t until Walter Schwartz sent me these pics.
He said “Behold the ingenious alidade, a surveying instrument here used as a fire finder. This one is displayed at the Cole Land Transportation Museum in Bangor, Maine. Forest rangers used these atop fire towers to report the distance and, in conjunction with another tower, the coordinates of fires. The map on this table covers an approximately 25 mile diameter (40 KM) inclusive of Augusta to Rockport Maine. The user viewed through a rectangular slot on one upright and rotated the metal structure to view the fire. Some tables were on slides so that the view would not be obstructed by parts of the tower structure. GPS and cameras solve the same problem today. “
Well who knew that? I found this great explanation of the alidade.
