In May of 1803, when purchasing supplies for the expedition he and William Clark were soon to lead through the Northwest, Meriwether Lewis bought four "tin horns" – elsewhere called "Tin blowing Trumpets" or, by Sgt. Ordway, "Sounden horns" – from Philadelphia tinsmith Thomas Passmore for 50 cents apiece. Judging from the price, they probably were of the type commonly used on eastern canals for signaling between boatmen and lock-tenders or wharf workers.
The expedition was to leave Camp Dubois, near St. Louis, Missouri, in May of 1804, in two large pirogues, and a custom-built 55-foot flagship they called "the barge," or more commonly "the boat," but never called a keelboat. The two pirogues were painted red and white, respectively, so they would be distinguishable at a distance, but when they were out of sight of the flagship horn signals may have been used to keep in touch. The horns also served to summon the men back to their boats for embarkation. On several occasions a horn was used to call in lost hunters, but we read of that mainly when it was unsuccessful. En route up the Mississippi from the Ohio on November 23 and 23, 1803, for example, Lewis employed gunfire and horn blasts to summon Nathaniel Pryor, who was overdue from a hunting assignment, but the signals weren't heard. When the signal worked, though, that wasn't newsworthy. Evidently the horns were used quite a bit from the very start, for Clark had to send a couple of them from Camp Dubois to St. Louis to be repaired.
On two occasions Lewis referred to the horn as a trumpet, but a trumpet would have had a cupped mouthpiece in which the player's lips would vibrate to set the air column in motion and produce a scale of two octaves or more.
Click to hear typical boatmen's horns.
The boatman's horn, however, had only a simple mouthpiece with a "reed" made of flexible metal, which vibrated when air was blown through it and produced a single pitch. It had no finger holes and therefore was useless as a musical instrument, although each horn possessed its own distinctive timbre and pitch, and with a little practice in blowing harder or softer, two or more tones, unique to each instrument, could be coaxed from it.
As a bonus, those boatmens' horns certainly made dandy New Year's noisemakers.