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Nautical time and civil date

Nautical time and civil date

[Editor Arthur R. Hinks of the Geographic Journal, annotated the following letters to the Editor in August 1935.]

A LETTER to the Secretary, Royal Geographical Society, from Mr. Thomas F. Milne, of Caulfield, Victoria, Australia, raised a number of interesting questions. He wrote:

" I should esteem it a great favour if you can furnish me with any information as to the precise time when navigators abandoned the old practice of making no adjustment to their ship's time (i.e. date) at the 180th meridian, and only did so when they entered the first civilized port. I suppose that old practice was discontinued at the instigation of some authoritative body, but nobody here seems able to give me any enlightenment on the subject. You will, of course, be aware that the old method was followed by Cook, but in recent days certain pedagogic oracles here in Australia have developed a mischievous propensity, as I regard it, of bringing the great navigator's ship time 'up to date.'

"That is to say, they bring his ship time, as it relates to his passage along Australia's eastern seaboard, into accord with calendar time as now observed in our eastern States - 10 hours ahead of Greenwich. In my opinion such a 'correction' of the logs of Cook, or any of the old maritime explorers, is pedantic and altogether unwarranted. If it is fitting to say - as an official publication, the Commonwealth Year Book, does say - that Cook, who was sailing 'West about,' made his Australian landfall at 6 a.m. on April 20th, 1770, the time shown on his log and journal being 6 a.m. of April 19th, it follows that it would be just as proper to deal in similar fashion with Cook's New Zealand dates, and the dates relating to quite a number of places he visited in course of his three voyages which only set up a civil calendar long after his day. For example, on his third voyage he was sailing East, and his ships were in 204 degrees East longitude at the spot where his career came to a tragic close.

"By his ship's time he was killed in the A.M. of February 14th, 1779, and that date is still universally accepted as the correct date of his death. But the longitudinal position of the two ships made them 13 hrs. 30 minutes ahead of Greenwich, whereas the Hawaian Islands are now reckoned to be 10 hrs. 30 minutes behind Greenwich. Are we therefore to say that the date of Cook's death, as we find it recorded in many books, and on many monuments, is incorrect to the extent of 24 hours; and that February 13th, not the 14th, is the true date of the tragedy?

"In short, endless confusion would inevitably ensue if the habit of tampering with Cook's logs which is growing up in Australia were to become general. ... Meanwhile, I should be very glad of any information you are in a position to give me as to when the globe was divided, for navigational purposes, into east and west longitudes at the 180th meridian, and at whose instigation the change from the old practice was brought about."

It will be convenient to distinguish the several questions by numbers. They are in effect:

I. When did circumnavigators abandon the old practice of reckoning their longitudes continuously from 0° to 360° east or west as might be?

II. And when did they adopt the present practice of changing the date on crossing the 180th meridian?

These two questions are evidently closely related, but the answer is not necessarily the same.

III. Is it permissible to change the dates entered in ships' logs, to conform with modern conventions?

In response to a request from Vice-Admiral Sir Percy Douglas, to whom Mr. Milne's letter had been referred, the Librarian of the Admiralty (Mr. D. B. Smith) very kindly went into the matter, so far as related to the practice in Cook's day, and gave us the following references to I:

Byron, on his arrival at Batavia in November 1765, says: "The next day, which by our account was the 28th, but by the account of the Dutch at this place was the 29th, we having lost a day by having steered westward a year..."

Wallis, after leaving the Cape of Good Hope for home, in February 1768, says: "On the 13th, having sailed westward 360 degrees from the meridian of London, we had lost a day; I therefore called the latter part of this day Monday, March 14th."

Krusenstern, in his 'Voyage round the World,' says: "On the 29th April (1806) we had made three hundred and sixty degrees of the Greenwich meridian from east to west. I therefore altered my reckoning; and as we had lost a day, called the next the 1st of May."

At least up to 1806, apparently, the practice was to carry on at sea until a whole day had been gained or lost, and then to make the change. While a ship was in port she might find her reckoning different from the port reckoning, but she did not alter it except perhaps temporarily. When was the practice changed? We have not up to this point found any reply to this question 11. As to I, Mr. Smith refers us to the International Meridian Conference, Washington, 1884, when the following resolution was adopted:

"That from this meridian (id est Greenwich) longitude shall be counted in two directions up to 180 degrees, east longitude being plus and west longitude minus."

But this merely confirmed what was already used extensively. At the request of Sir Percy Douglas, the Hydrographer of the Navy caused a search in the early charts of his departmental collection, and has kindly supplied a list of examples which may be summarized thus:

A. Division continuously East or West from Prime Meridian


MS. Spanish Charts

275° to 320° E. of Ferro


Cook's first voyage: East coast of Australia and New Zealand

205° to 210° W. of Greenwich


North America: H. Hanwell

65° to 204° W. of Greenwich


World Chart: Arrowsmith

0° to 360° E. of Greenwich


Track of Pandora

105° to 240° W. of Greenwich


B. Division East and West of Prime Meridian


Commodore Byron's track . . . . 83°W. to 169°E. of Greenwich


Cook's second voyage: Gilbert's charts 0° to 180° E. and W. of Greenwich


Hydrographie françoise0° to 180° E. and W. of Paris


Atlas maritimo: Tofino E. and W. of Cadiz


Pacific Ocean: Arrowsmithto 180° E. and W. of Greenwich


Track of Albemarle and Gorgonto 180° E. and W. of Greenwich


World: Laurie and Whittle0° to 180° E. and W. of Greenwich


Track of Cornwallis65° W. to 160° E. of Greenwich


Track of Comet130° W. to 147°E. of Greenwich

There is thus no evidence of any clearly defined change in the reckoning of longitude [1]: the custom altered gradually between 1750 and 1800 and the older method survived into the nineteenth century. Two track-charts of Captain Colnett's voyage round the world, published in 1802-03, are graduated respectively from 30° W. to 195° W., and from 30° W to 168° E.; while a World Magnetic Chart by T. Yeates is graduated to 360° E. at the top and to 180° E. and W. at the bottom.

For the history of the Prime Meridian we may refer to the article by Mr. W. G. Perrin in The Mariner's Mirror for April 1927. The earliest maps on which he was able to find the Greenwich meridian as the origin of longitudes were two charts attached to the 'Description of the Sea Coast,' by Fearon and Eyes in 1738, and the 'Survey of the County of Oxford,' by Thos. Jeffreys, published in 1769. The meridian of Greenwich was used in the magnificent collection of charts, the 'Atlantic Neptune,' published from 1777 onwards: and thereafter it soon superseded all others in English maps and charts.

Before dealing with question III we must refer to a complication which is fundamental, though it does not appear in Mr. Milne's letter. Mr. Smith writes:

So far as I know, the only thing historians in this country do is to alter nautical time to civil time. Till 1805 logs were kept in nautical time; that is to say when they were written up at mid-day, that day's entry consisted of the proceedings for P.M. of the day before and A.M. of that day. [2] The change was ordered by Admiralty Circular of 11th October 1805 which ordered that "the calendar or civil day is to be made use of, beginning at midnight." The orders reached the Mediterranean Fleet too late for Trafalgar, so that the Trafalgar logs are in the old form; and the Admiralty Trafalgar Committee (1913) put this explanation in their Report: "In 1805 the Nautical day commenced at noon, twelve hours earlier than the civil day. The proceedings given in the Logs as for 20th October are really the proceedings for the afternoon of the 19th, followed by those for the morning of the 20th civil time. ... Similarly, the details of the Battle are shown in the Logs under "22nd October P.M." The Private Diary of Lord Nelson was kept in civil time.

We find Cook's journals kept the same way, and in editing the journal for the first voyage Admiral Wharton reproduced Cook's own "Explanation" (from Journal) which begins " It is necessary to premise by way of explanation, that in this journal (except while we lay at St. George's Island) the day is supposed to begin and end at noon, as for instance, Friday the 27th May, began at noon on Thursday 26th and ended the following noon according to the natural day. . . "

The official narrative, got out under Admiralty order, of Cook's last voyage narrates the circumstances of Cook's death under Sunday, February 14th, 1779. Captain King says that Cook left for the shore "between seven and eight o'clock;" he means A.M., so that the incident should be recorded in the Ships' Logs for the 14th when made up at mid-day on the 14th, and this is so. Lieutenant-Commander Gould published in The Mariner's Mirror (the journal of the Society for Nautical Research) for October 1928, transcripts from these logs and journals in 'Some Unpublished Accounts of Cook's death.' The Discovery's log for Sunday 14th first gives P.M. events (that is, what happened between mid-day on the 13th and midnight), then A.M. events (including the report at 9 A.M. of Cook's death). It is the same with the other logs and journals he reproduces.

There were thus in use in the Navy until 1805 three days: the nautical, the civil or natural, and the astronomical. The nautical day entered in the log as May 10 began at noon of May 9 of the civil reckoning, and P.M. thus came before A.M. On the other hand, the astronomical day of May 10 began at noon of May 10 by civil reckoning, and ran from 0h to 24h ending at noon on May 11. This was the time used in the Nautical Almanac, first published in 1767, and this was the time kept by Mr. Charles Green, the astronomer on Cook's first voyage. Though it must have been in continual use in the navigation of the ship, it does not appear in the logs. But it must be borne in mind as a possible source of confusion.

The log was kept in ship's time, that is, the local apparent time, adjusted at intervals to the change of longitude: and by old practice an adjustment was made at noon, when the officer taking the latitude sight called "Twelve o'clock, Sir," and the Captain said "Make it so," (though the actual observations for local time were necessarily made morning and afternoon). If it were necessary to establish the accurate time of an event we should have to enquire more particularly whether the time of the nautical day was on that ship carried on from the noon on which it began, or adjusted to the noon on which it ended, or perhaps altered during the night from one to the other, as is more or less the present practice in merchant ships, though H.M. Navy keeps Standard Time. In default of better information we may without serious error (in days of sail) take the recorded hour as in the apparent time of the meridian of longitude mentioned in the account, and for form's sake apply the equation of time to reduce to civil time of the meridian.

If any one should require to go beyond the day and hour of the log, the only safe procedure is to reduce to Greenwich Civil Time: after which we can if we like argue securely about what would have been the date if the voyage had been made the other way round, or if the present rules for change of date had been followed then. The process is best studied in examples. Let us discuss the dates of Cook's landfall on the south-cast Coast of Australia, his landing at Botany Bay, and his death in Hawaii.

Cook's Landfall, 1770

On his first voyage Cook sailed west, and kept his longitude west of Greenwich. The land he estimated as in long. 211° 7' W., or 14h 4 ½m, say 14h. We have then for the date of landfall:

Journal Thursday 19 April 6 a.m. = Ship's Apparent Time April 19, 6h
Adding the long. W. this is Greenwich Civil Time April 19, 20h.
The Equation of Time is on this date less than a minute, and is here neglected.

Cook's Landing at Botany Bay

Journal Sunday 29 April P.M. = Ship's Apparent Time say April 28, 15h.
                              = Greenwich Civil Time April 29, 5h

If in 1770 Cook had been keeping the time which is now Standard in New South Wales, 10 hours fast on Greenwich, he would thus have made his land-fall on Friday, April 20, at 6h, and his landing at Botany Bay on Sunday, April 29, at 15h, and these dates, April 20 and April 29, are adopted in the Official Year Book of the Commonwealth of Australia. Number 22 for 1929, page 3, says that Cook sighted the Australian mainland on April 20 at 6 a.m., discovered Botany Bay on April 29, and landed on the following day. Number 25 for 1932 corrects this, and says the arrival and landing took place on the same day, i.e. 29 April, 1770. The Australian Encyclopaedia, vol. 1, p. 432, says: "At daybreak on 20th April, 1770, he sighted land. . . . At 2 P.M. on Sunday, 29th April, the Endeavour anchored in Botany Bay. At 3 P.M. Cook landed." This is what our correspondent calls "the mischievous propensity of bringing the great navigator's ship time up to date."

Cook's death

On his third voyage Cook was sailing East about and the longitude of the place in Hawaii where he met his death is about 204° = 13h 36m East of Greenwich. He went ashore on "Sunday, February 14 between 7 and 8 o'clock." Supposing that he was killed at 8 o'clock by this reckoning we have:

Journal Sunday 14 Feb. 1779, 8h = Ship's Apparent Time Feb. 14, 8h
Applying the Equation of Time, 14m, this is Local Civil Time Feb. 14, 8h 14m
Subtracting the Long. East 13h 36m, this is Greenwich Civil Time Feb. 13, 18h 38m or in the present Hawaii Civil Time (10h 30m slow on Gr.) Feb. 13, 8h 8m

That is to say whereas the narrative says that he was killed on a Sunday morning, it was only Saturday evening at Greenwich, and would have been Saturday morning in the narrative if Cook had been sailing West about instead of East about.

The important point seems to be that in the reckoning of the whole voyage he was killed on a Sunday: and that if the historian tampers with the dates of the principal events in a voyage, he throws them out of relation to the remainder of the narrative. We are therefore disposed to agree with our correspondent, that it is mischievous to bring historic events "up to date" in time reckoning.


[1] [Added by this Society's staff] Articles by J J O'Connor and E F Robertson on Longitude and the Académie Royale discussing Longitude on land, and on the English attack on the Longitude Problem discussing the further developments for mariners' uses.   [back]

[2] The standard text-book on navigation in Cook's day was J. Robertson's 'Elements of Navigation.' The following quotation is from the 4th edition (1780), revised by William Wales, 11, 315-6: "The Log-Book is a book ruled like the log-board, in order to contain the daily copies of the remarks written on the log-board, which is the only authentic record of the ship's transactions; and these are by the persons who keep Journals transcribed every day at noon into their log-books, from which they make the necessary deductions relative to the ship's place . . .

". . . Mariners reckon time in the astronomical manner, beginning at noon and counting from thence 24 hours to the next noon. The first 12 hours, from noon to mid-night, they mark with P.M., signifying after mid-day; and the second 12 hours, from mid-night to noon, they mark with A.M., signifying after mid-night; and end their day's work on the noon of the nominal day. Hence their ship account is 12 hours earlier than the civil account of time. . . . Thus that day's account which is marked Sunday the 9th of October, began on Saturday noon, and ends on Sunday noon."   [back]

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