DAVID THOMPSON IN
PEND OREILLE COUNTRY
David Thompson (1770-1857) was a fur trader, surveyor, mapmaker and explorer for the Hudson's Bay Company and later for the North West Company. Between the years of 1808 and 1812, Thompson spent much time in the Pend Oreille and surrounding area and erected the first European structures in what are now the states of Montana, Idaho and Washington, together with surveying and mapping the entire main stem of the Columbia River and parts of the Kootenai, Clark Fork, Pend Oreille, Flathead and Spokane Rivers as well.
Upon his arrival in this region in early 1808, Thompson surveyed and mapped the Kootenai River from Canal Flats, British Columbia all the way through Montana and Idaho to Kootenay Lake, BC, portaging around Kootenai Falls. He made many celestial observations for latitude and longitude while in the vicinity of present day Bonners Ferry, Idaho.
Thompson returned to this area in 1809 and established "Kullyspel House" on the Hope Peninsula in September of that year. In November Thompson established another trading post called "Saleesh House" near present day Thompson Falls, Montana where he spent the winter. In 1810 he had his traders construct "Spokane House" near the mouth of the Little Spokane River.
In 1811 he became the first person to travel, survey and later map the Columbia River from its source near Invermere, British Columbia to its mouth at Astoria, Oregon, adding the Columbia River as the final leg of the Fur Trade Highway from Hudson's Bay and Montreal to the Pacific Ocean. He spent the winter of 1811-12 at Saleesh House near Thompson Falls, MT and then left the area for Montreal, Canada. He would never again cross to the west side of the Rocky Mountains.
Between 1817 and 1826 Thompson reached the epitome of the surveying profession while serving as "Chief Surveyor and Astronomer" for the British Commission to establish the international boundary between the United States and British processions from the lake of the Woods, through the Great Lakes, to the Eastern Townships of Quebec.
SURVEYOR AND CARTOGRAPHER
The Columbia Plateau was basically unknown outside its undefined boundaries and unmapped until David Thompson's time. He filled in the map from Lake Superior to the west coast. Thompson was well versed in the science of practical astronomy that used knowledge of the position and movement of certain astronomical bodies (the sun, the moon, moons of Jupiter, navigational planets and the brighter fixed stars) to locate one's position on the surface of the earth. To accomplish this, he used a sextant, pocket chronometer, mercury filled artificial horizon and astronomic tables (ephemerides) to determine the LATITUDE (distance north of the equator) and LONGITUDE (distance west of the Greenwich Meridian) of key positions, such as fur trade post sites, river mouths, mountain passes and other topographical features.
SEXTANT
The single most important surveying instrument in Thompson's possession was his sextant which he transported in a cork-lined box. It was designed to measure angles both vertically; generally the altitude of the sun, other star, moon or planet above the horizon to establish LATITUDE and horizontally (on its side); for measuring the angle between the moon, sun, other star or navigational planet to establish LONGITUDE.
MERCURY REFLECTING ARTIFICIAL HORIZON
Because the ocean or other large body of water was usually not available to land-based explorers to use as a horizon, they had to use an artificial horizon consisting of a trough containing mercury, the surface of which served as a reflector. A glass roof (parallel glasses) was placed over the trough to prevent the wind from affecting the mercury's smooth surface. The mercury was stored in an iron or wooden bottle.
From the History Marker