Osborne Fire Finder

Mr. Osborne also designed the photo-recording transit for making panoramic records of forest conditions, as well as a collapsible water-bag knapsack for firefighting (patented in the US in 1935).

The system is composed of a topographic map of the area oriented and centered on a horizontal plane table with a circular rim graduated in degrees (and fractions).

Two sighting apertures are mounted above the map on opposite sides of the ring and slide around the arc.

The fire lookout notes the degrees on the graduated ring beneath the sight.

Early Fire Finders were capable of a crude estimate of elevation based upon the level and elevation of the table, calculating distance and rough position of the fire by reference to any distinctive terrain features and by use of the scale shown on the map.