NavList:

It is highly improbable that James Cook used lunar distances to obtain longitude --at least at sea at the time. Our late friend George Huxtable – whose many contributions and lively discussions on NavList some members may remember – has analyzed Cook’s Atlantic crossings in 1764 to 1767 (“Journey to Work: James Cook's Transatlantic Voyages in the Grenville 1764-1767”, in: Journal of Navigation, Vol. 63 (2010), 207 – 214) and found that Cook used dead reckoning to find his longitude. And Charles Green, the astronomer on Cook’s first voyage wrote to the secretary of the Royal Society on 28 November 1768: “I thought it a little odd when I found that no person in the ship could either make an observation of the Moon or calculate one when made.” “No person” apparently included Cook, who – as his biographer Beaglehole wrote, showed “a more lively interest”, without being able to say exactly when he learnt the technique (Beaglehole, The life of Captain James Cook, Stanford, Calif. 1974, 116). So it is also unlikely that Cook practised the lunar distance method when charting in North America.

Best
Wolfgang