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Among explorers in Africa, many shot lunars, including Dr. Livingstone, I presume. 

Actually we need not "presume", though I couldn't resist the referential humor. David Livingstone famously stayed up late into the night shooting lunars to get longitudes in Africa as often as he possibly could, even when he was ill. It's a funny thing though. By the time these lunars were analyzed for accurate longitudes (which was not necessary on site and could be done back in England), it was usually too late for any practical significance. The telegraph quickly followed any exploration that led anywhere with commercial or strategic value. And once you have a telegraph line in town, you have a near-perfect source of GMT. Lunars are then superfluous. Nonetheless, explorers, both professional and amateur (here in the derogatory sense of amateur), were strongly encouraged to make lunar observations. Longitude "by lunar" was certainly close to obsolete by 1880 even in land exploration. Certainly at sea lunars were effectively dead and buried by 1850.

I can't recall if I said this recently. Many people who take up an interest in navigation history do so from a science or engineering or mathematics background, myself included. But we have to avoid thinking like mathematicians. In math, one exception completely falsifies any theorem. History is not like that. History is about general trends, statements founded on a preponderance of evidence, and exceptions are always present. So when I say lunars were "dead and buried" at sea by 1850, that doesn't me you can't find someone in each and every decade that follows in some vessel somewhere who was still shooting lunars. After 1850 lunars at sea were a peculiar exception, popular with eccentrics and old men, no longer common or even uncommon practice.

And yes, David Thompson shot lunars for longitude in Canada with great success. That's all the more reason to scoff at the Lewis and Clark expeditions low competence in lunars just a few years later ...south of the border.

Frank Reed
ReedNavigation.com
Conanicut Island USA