NavList:

Henry H wrote:

"I certainly so not question the evidence produced by actual voyage log
books, but do wish to remind all hands of Thomas Arnold's work both in
publishing and in conducting a school intended to educate the mariner in
working Lunar Distances. As I have previously noted on this List,
Bowditch was not alone in the advocacy of Lunars in the USA - Arnold,
certainly a commercial vessel navigator, states having utilized them over
a 40-year period as Master of American vessels, and in the 1820s wrote
rather prolifically on the subject and actually operated a school at
Philadelphia."

 

On your recommendation, I acquired a copy of "Arnold's Lunarian" and I agree that it is a very interesting textbook. But classroom recommendations are just that. Arnold and Bowditch are clearly writing to one another as much as to practicing navigators. There were back then people like ourselves who simply loved lunars in every way --Nathaniel Bowditch was certainly in this category. But practice is different from teaching. In practice, lunars were mostly shot using the Sun and usually for a two or three day period around First Quarter or Last Quarter. Thus they provided a check on the primary method of determining longitude rather than being a primary method in and of themselves. Before about 1830/40, the primary longitude was the dead reckoning. After that, it was the chronometer longitude. And just a decade or two after that, lunars were essentially dead.

And wrote:
"It would be of interest to consider whether all navigation calculations
actually done aboard any particular vessel, aside from a notation of
position, was actually spread out on the pages of the log book, as
opposed to being calculated on scraps of paper or in a separate workbook
which remained the possession of the individual - of course it involves
an entirely different era, but I still retain volumes of navigation work,
of which only the resultant position ever found its way into the logbook.
As they say, however ..."Different ships, different longsplices"."

 

Yes. I posted just this week an example of a complete worked lunar from a blank page in a logbook (he's using this blank page a couple of years after the voyage recorded in that logbook). See the thread "A Lunar from the 1840s". I also posted a similar worked lunar from the 1820s a couple of months ago.

 

Though there are cases where navigators wrote up all their lunars in detail with all of the calculations and displayed them in their logbooks (out of vanity, I would say), for the most part the only detail given is the resulting longitude and usually some indication of the other body (e.g. "Moon-Antares" or "Moon-Sun"). In almost every case, there is unambiguous information in the logbook which states how the longitude was determined. Among the entries:

1) "Long by DR"

2) "Long by acct" (same as dead reckoning)

3) "Lon in" (same as dead reckoning)

3) "Long by Lunar" (in most cases with some further details in the margins)

4) "Obs Lon" (this one is tricky. It's a rare usage and might be ambiguous, but it's been possible to prove in every case I've seen that this is an early expression for a longitude by time sight, in other words a chronometer-derived longitude).

5) "Long by Chr", "Lon by Chrono", etc.

6) "Lon" (this becomes common after 1850-60 because by this date navigators are using chronometers almost exclusively).

 

But you always have to check carefully. In a couple of logbooks, I have seen evidence which could easily be misinterpreted as extensive, daily use of lunars. One navigator, aboard the Brig Reaper, which was a central part of the presentation I made on lunars at Mystic last June, used "Lon Lunar" to indicate a separate dead reckoning which he carried forward (for over a month in one case) from his last lunar. This is clearly the case because the changes in the "plain" DR longitude move in lock-step with the "Lon Lunar".