NavList:

Frank, in your 10Feb2024 posting, you wrote: "Consider this ... he didn't have to calculate a single one.  He could have simply brought the observations home . . . and work out the longitude after all observations had been collected."

I took this good advice as a guide in searching for further astromonical measurements with longitude-determining potential.

Cook made the 1766 Burgeo measurements knowing what field measurements were needed but he was also aware that measurements of the eclipse were required with respect to a reference meridian back in England.  In the off-season Cook kept the Grenville (his survey schnooner) at Deptford on the Thames just a short walk away from the Greenwich Observatory where Nevil Maskelyne (the Astronomer Royal) laboured away preparing the nautical almanac that was first published in 1767.  I think it's reasonable to presume that Cook and Maskelyne would be aware of each other's work.  Cook's survey work was actually an important military mission, so he would have been able (perhaps backed up with orders) to access/obtain whatever information he needed.  So, I think it's not unreasonable to assume that Cook knew that the information needed to estimate longitude was "in the works" and took the astronomical measurements at Burgeo (and possibility elsewhere) for use at some later time to estimate longitude and thus retro-position his latitude-only charts in a global latitude/longitude grid (as patently shown by the Cook-Lane 1775 map that was published showing latitude 'and' longitude).  

Cook made the Burgeo eclipse measurements likely with an awareness of Maskelyne's activities; however, he would likely 'not' have known about Hornsby's Oxford eclipse measurements.  Upon returning to Deptford in the fall of 1766, Cook's friend Dr. Bevis became aware of Cook's eclipse measurements.  Bevis showed them to George Witchell who was aware of Rev. Hornsby's eclipse measurements in Oxford.  This 'friend-of-a-friend-of-a-friend' sequence may seem highly speculative but 'longitude determination' was THE topic of the time and there was big, big prize money on offer by the Board of Longitude.  The fact that the Cook-Bevis-Witchell-Hornsby interaction chain was explicitly reported in the 1767 publication in the Philosophical Transactions of the Royal Society (attached) indicates that the interaction was of far greater import than mere coffee shop banter.

The Royal Society's publication of the data for the Burgeo eclipse certainly brought to light that Cook might have been taking some extra measurements now and then in the course of his survey work; perhaps doing so in anticipation of using them to estimate longitudes at some future time.  So, the question arises: at what other locations and times would Cook have had similar astronomical opportunities along with having sufficient visibility to take longitude-related measures?  

The locations where he took noon sights for latitude determination are possibilities.  At least the noontime visibility at those times and dates can be presumed to be reasonably good.  But, was the moon "in distance" at any of those times and had the date been logged for the noon sight?  If so, then Cook would have witnessed a 'lunar'.  

I've been scouring the information sources thus far available to me in hopes that these sorts of opportunities could be identified. Thus far, I have found just one: Cape Norman.  John Robson, in a report posted to the Captain Cook Society website about Cook's 1764 activities, tells us: "On 2 August, Grenville stood off Cape Norman, the most northerly point of Newfoundland . . . [where] Cook went ashore . . . to take the sun’s meridian altitude."  

I fired up Stellarium and pointed it to Cape Norman for Aug 2,1764 and fiddled things until the Sun reached local apparent noon (Sun's HA as close to 0h0m0sec as possible) and, as seen in the screen shots in the attached PDF, I was presented with the Moon "in distance" to the southeast.  If Cook took the appropriate measurements, then a longitude estimation could be performed at some later time.  

Andrew David in a 2009 article in the Northern Mariner reports that "[Cape Norman] was one of six places where Cook took such observations during his 1764 season."  I think I have spotted many of the other locations but specific dates for each location still elude me.

Cheers,

Jim.

PS. The 'CMI' mentioned in the attached PDF refers to the Coastal Marine Informatics 'spatial directory' for Cook's Newfoundland voyages in the 1760s.  Here's it is: CMI. Cape Norman may be 'found' in three ways: (1) start typing norman (no quotes) in the search box at the upper left; by the time you've typed 'nor', 'Cape Norman 1764' will appear as the first item in the leftside listbox, or (2) scroll down the items in the leftside listbox until you come to 'Cape Norman 1764', or (3) you can pan and zoom to find it in the rightside mapbox.  Click its 'blue dot' and more info categories will be revealed for 'Cape Norman 1764'.