Antique ships' logs contain valuable details of past conditions at sea.

Ships’ captains kept daily records of exact location and weather conditions. Whalers would also record sightings and capture of all species of whale they came across.

Sextants and Chronometers

• In the eighteenth century the accurate determination of latitude was possible with the use of sextants (and smaller octants) which could measure the elevation of the sun at noon each day. Longitude was much more difficult, and had to wait until reliable ships’ chronometers became available towards the end of the century. With a chronometer recording Greenwich Mean Time it was easy tell how much earlier or later the sun reached its zenith, thus establishing the longitude.

• Before sextants and chronometers became available navigators relied on a variety of less accurate instruments for estimating latitude (the backstaff and the cross-staff), and longitude was estimated by dead reckoning. (Although Nautical Almanacs allowed sextants to convert the angular distance between the sun and moon to estimate time from 1767 – this method of calculating longitude rivalled chronometers for a while, but the clocks won out in the end.)

Whale Sightings

The daily recording of location, weather conditions and whale sightings by early whaling captains allow us to piece together details of population numbers, distribution and migration patterns of many whale species, before whaling took its toll.

Other Information

• All ships kept a log of some kind, and those of British Naval vessels are particularly informative. In addition to recording weather conditions and location daily, in shallow waters the depth was routinely measured. This was done with a lead-line, and there was usually a piece of tallow inserted in the bottom of the piece of lead. When the lead was swung aboard it was easy to see what sort of material was stuck in the tallow, allowing accurate records to be made, not only of depth, but also of the nature of the sea-bed (mud, rock, grave, sand etc.).

• The accurate weather information gives a good base-line against which we can compare modern weather and begin to assess changing conditions. Information about the nature of the sea-bed is also useful, particularly when naturalists caught interesting specimens in the same locations.

Nautical Memorabilia

• Anything that can be reliably associated with particular vessels or individual mariners is collectible. (Pieces of Nelson’s ship ‘Victory’ that can be proved to have been there at the time of the ‘Battle of Trafalgar’ have enormous value!). Collectors seem to like old navigational equipment best (antique sextants and chronometers), but many old log-books are also in private hands.
• As with detailed information from shell collectors, it would be good if those in possession of antique ships’ logs could publish some of the contents, particularly those with references to sightings of whales. (See discussion)

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