NavList:

I think that my point may not have been clear (or that it was easy to misinterpret) in the original post in this thread. I am not trying to suggest that lunars were not used. They were. But they were used in a very different fashion from what many people suppose. In the period before chronometers became common, there was no "lunars era" in which lunars were the PRIMARY method of determining longitude for most navigators. Instead, lunars were treated as a check on the dead reckoning, something to consider IN ADDITION TO the longitude by dead reckoning which was the primary longitude for the vast majority of navigators.

 

Starting in the 1830s there is a "sea change" (you could also call it a "paradigm shift") in the way navigators recorded and discussed their longitude. The longitude by chronometer was "it" for most navigators. They used dead reckoning only for brief periods of a day or two when observations were impossible. And for a few decades they continued shooting lunars as occasional (typically twice a month) checks on the longitude by chronometer. This is a radical change from the earlier period when the dead reckoning was carried on for months at a time.