May 11, 1793. Achrometer.

Alexander MacKenzie, May 11, 1793. (from his Journal, Day 3 of the epic voyage)

“The weather was overcast. With a strong wind a-head, we embarked at four in the morning, and left all the fresh meat...the canoe already being too heavily laden.”

    

     Although the explorer noted losing his pocket-compass in the water yesterday, he doesn’t say if he has a spare one or not. I’m assuming he did, however, because his recorded directions of travel remain just as accurate, as the voyage continues. The photo I’ve chosen is of an 18th century pocket-compass, made in England, and likely very similar to the one he lost.

     Over various observations made during his time at Fort Fork, MacKenzie had determined that his “achrometer” was 1 hour forty-six minutes slow to apparent time, at his departure on May 9th: so he had determined it to be 22 seconds slow, in 24 hours. Although I’m not sure which one he actually used, chronometers were already quite advanced technology in 1793. He may have used one like the one shown here from 1763. He needed accurate timekeeping for his reckoning.

     Navigators of the day determined their latitude, usually with incredible accuracy, by measuring the sun’s angle at noon, when the sun is highest, and/or by measuring the angle of the North Star from the horizon. Determining longitude however, was in those days was a different matter. On his last trip to England he had studied astronomy and navigation, and there he learned to observe the moons of Jupiter. Discovered and observed by Galileo, the satellites of Jupiter orbit the giant planet at a predictable and rapid rate, and can be observed by the navigator on Earth and then used as a celestial “clock”. His “Cassini Tables” told him the precise time (at Greenwich on any given day) when the moons of Jupiter would transit or eclipse. The difference between that and his actual time wherever he is, allowed him to determine longitude. This was the method used by land navigation and cartographers in the 18th century. It did not work on the ocean, however, as the satellites of Jupiter were too hard to see from a moving ship. I think MacKenzie had a really high quality telescope; and certainly there was no "light pollution" in those days.

     Using Google Earth, I have found that his Lat measurements for the winter Fort were very close, and his longitude only out by about 8 miles. Not bad for this vintage technology!

     The journey on the river on May 11 is against an increasing current, with 14 miles attained until running the canoe onto a “stony flat”, after which repairs to the canoe were required. 

     The encampment of this day was at or near the mouth of The Burnt (Saddle) River, (which drains the areas we know as Spirit River, Rycroft, Woking, Wanham etc.), about 10 miles SE of present day town of Bluesky, Alberta. This is where he meets a Chief of the Beaver Indians, who are on a hunting party. MacKenzie’s hunters asked permission to go to the native lodges and stay overnight with them, which they did. MacKenzie visited with the Chief and his friends until late…“It was near twelve at night when he took his leave, after I had gratified him with a present of tobacco.”