Osborne Firefinder

Many Thanks to to Mr. Ray Kresek for allowing us to re-print this article. Please visit the Fire Lookout Museum at 123 W. Westview in Spokane, Washington, 99218, or phone (509) 466-9171; or visit their web site at http://www.firelookouts.com

The Osborne Firefinder by Ray Kresek

William Bushnell "Bush" Osborne, Jr., as a young graduate forester, went to work for the U.S. Forest Service in 1909 on the Oregon National Forest at Mount Hood.

In 1911 he invented an alidade he called the "firefinder" and tested in at 8 locations in Oregon and SW Washington. The original instrument was 14" across, round, with a map of the surrounding area, and each of 360 degrees etched around the rim. This disc was secured to an 8-sided 1/8" steel base which was in turn secured firmly to a tree stump. A brass sighting mechanism consisting of a rear vertical slit and a front vertical horse hair stretched tight, pivoted precisely in the center of the circle. The location of the lookout point was situated exactly in the center of the circular map. An arrow etched beneath the rear sight corresponded with the compass reading when the sights lined up on distant smoke.

This first Osborne Firefinder was commercially produced in 1913 by Fred Leupold and Adam Volpel (Leupold-Volpel & Co.) at their scientific instrument manufacturing facility in Portland (Oregon).The U.S. Forest Service purchased fewer than 100 of these 1913 Model Osborne firefinders.

In 1914 the center-pivot sighting mechanism was abandoned in favor of a circular outer ring with the original fore and aft sights affixed to it. A cast iron base with a round recessed rim permitted the signts to be moved freely around the rim. Zero degrees was positioned true S[outh] from the lookout location. To prove this instrument, "Bush" Osborne placed it atop Mount Hood the following summer. In one month lookout Elijah "Lige" Coalman spotted and reported 131 fires with this instrument!

In 1915, Osborne again modified his "firefinder" sighting mechanism. The 1915 model featured a 0-power scope similar to those used on a rifle, instead of the original fore and aft upright sights, to peer through. Precision calibration permitted obtaining azimuth readings to 1/60th of 1 degree; and a vertical angle reading in 1/10th of 1 degree accuracy. Several hundred of the 1915 Osborne Firefinders were produced by Leupold-Volpel Co.

In 1917, Bush Osborne again gave his Firefinder a radical change. Its width was enlarged from 14' to 24" across. Its weight was increased from 10 to 70 pounds, including the 3-railed track it sat upon. It featured rugged alidade sights front and back, using the concept of the 1913-1914 models; however, the front sight is equipped with a thin brass tape which could be moved up and down freely with a thumb wheel. As this wheel was turned back and forth while the observer sighted through the rear sight slot at the distant topography, a pencil attached to a sliding gear-driven arm could draw the panoramic features of the horizon. Thus, a panoramic picture could be drawn to accompany "seen area" maps made by the firewatcher. About a hundred 1917 Osborne Firefinders were manufactured.

In 1934, Osborne again radically changed only the sighting assembly, to include a far more simple mechanism. The rear sight now included "+" (plus) and "-" (minus) vertical scales and two sets of cross threads of horse hair, so that accuratae vertical readings could be made on fires both below and above the lookout's elevation. Leupold-Volpel Co. manufactured more than three thousand of the lighter weight 55 pound 1934 Osborne Firefinders, until it ceased to produce the instrument in 1989.

For a time prior to that, the A. Lietz Co. of San Francisco also manufactured the Osborne Firefinder in small quantities. The 1934 Osborne Firefinder is the most widely used fire plotting instrument in the world today. It is is used acoss America, and in many foreign nations on at least four continents. They were last featured for sale in the 1991 Forestry Suppliers catalog for $3,495 each.



Alidade: 1. An indicator or sighting apparatus on a plane table, used in angular measurement. 2. A topographic surveying and mapping instrument with a telescope and graduated vertical circle.

Azimuth: 1. The horizontal angular distance from a fixed reference direction to a position, object, or object referent, as to a great circle intersecting a celestial body, usually measured clockwise in degrees along the horizon from a point due south.





https://www.fs.usda.gov/detail/r1/fire-aviation/?cid=stelprdb5108647