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Last week I visited the research library at the Consitution Museum and viewed microfilm copies of several ship's logs, looking particularly for entries related to navigation.

For the period from 1810 to 1812 under Captain Isaac Hull, the format was the standard table of 24 lines, numbered by the hour from 12 noon to 12 noon. The columns included speed in Knots and Fathoms (fractions of a knot), course, wind, and Remarks. At the bottom of the table there was generally an entry for Latitude Observed, though on some days it was blanked. There were not any notations for longitude, either by observation or dead reckoning that I observed on any pages.
This lack of recording of longitude was surprising to me, and I have no explanation for its absence.

I also looked at an earlier log from 1803, during which time the Constitution made its first Atlantic crossing under Captain Edward Preble at the beginning of the Barbary Wars. The format was much the same as above, except that there was a single page near the beginning that recorded the navigational data for the crossing from 15 August to 6 September. There was one row for each day, and the columns were labeled Date, Courses corrected, distance, differences latitude, departure, meridian distance, longitude by dead reckoning, water.

The corresponding daily log pages had latitude observed in most cases, but again there was no indication of any measurement of longitude.

On 5 September, Cape St Vincent was observed from the ship. The longitude by prior dead reckoning was 13* 15' W. It was corrected to 8* 49' W from the observation of the Cape, a difference of about 213 nautical miles.

On 6 September, there is a notation of 'sailing by chart'. The following period, the ship enters the Mediterranean, and I saw no further observations of latitude or longitude.

The next logbook that I examined was for 1814-1815, Captain Charles Stewart.
These pages were more like what I expected. After the hourly accounting for each day, there was a single row form with column headings for
Course, distance, diff lat, departure, lat by acct, lat by obs, long by acct, long by chronometer, long by obs, variation

Generally, there was an entry for longitude by account for each day, but entries for chronometer and observation were less frequent. The first chronometer entries were in Feb 1814. I noted the following days in which lunar observations were also made, from March 1814 until Feb 1815:

Date Acct Chron Obs
14 Mar 79*56', 80*04', 80.*21'
27 Mar 58*20', 58*25', 58*24'
03 Jan 64*59', 62*38', 62*50'
04 Jan 65*06', 63*27', 62*58'
20 Jan 38*46', - 38*00'
01 Feb 14*30' - 14*11'

Of the lunar observation entries, two were made within two days of the first quarter moon, and four were made within one day of the last quarter moon.

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