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Cooks optegnelser

Keld Gammelgaard har fundet tekst fra Cooks skibsdagbogs-notater, der føles interessante og nærværende i den forstand, at kendte usikkerheder opstår.

Første observation er på vej fra England til Kap det Gode Håb, mens anden observation er på kanten til isen efter passage af Det Gode Håb. Det omtalte Kendals ur er en direkte kopi af Harrisons H4(note KG)


With these winds we advanced but slowly; and, without meeting with anything remarkable till the 11th of October, when, at 6h 24m 12s, by Mr Kendal's watch, the moon rose about four digits eclipsed, and soon after we prepared to observe the end of the eclipse, as follows, viz.

h. m. s.

By me at 6 53 51 with a common refractor.

By Mr Forster 6 55 23

By Mr Wales 6 54 57 quadrant telescope.

By Mr Pickersgill 6 55 30 three feet refractor.

By Mr Gilert 6 53 24 naked eye.

By Mr Hervey 6 55 34 quadrant telescope.


Mean 6 54 46-1/2 by the watch.

Watch slow of apparent time 0 3 59


Apparent time 6 58 45-1/2 end of the eclipse.

Ditto 7 25 0 at Greenwich.


Dif. of longitude 0 26 14-1/2 == 6° 33' 30"

The longitude observed by Mr Wales, was

By the and Aquilae 5° 51' |

By the and Adebaran 6° 35 |Mean 6° 13' 0"

By Mr Kendal's watch 6° 53 7/8


Though the weather continued fair, the sky, as usual, was clouded. However, at nine o'clock the next morning, it was clear; and we were enabled to observe several distances between the sun and moon. The mean result of which gave 39° 30' 30" E. longitude. Mr Kendal's watch at the same time gave 38° 27' 45" which is 1° 2' 45" W. of the observations; whereas, on the 3d instant, it was half a degree E. of them.

In the evening I found the variation by the mean of azimuths taken with Gregory's compass to be 28° 14' 0"

By the mean of six azimuths by one of Dr. Knight's 28 32 0

And by another of Dr Knight's 28 34 0

Our latitude at this time was 63° 57', longitude 39° 38-1/2"

The succeeding morning, the 15th, being then in latitude 63° 33' S., the longitude was observed by the following persons, viz.

Myself, being the mean of six distances of the sun and moon 40° 1' 45" E.

Mr Wales, ditto 39 29 45

Ditto, ditto 39 56 45

Lieutenant Clerke, ditto 39 38 0

Mr Gilbert, ditto 39 48 45

Mr Smith, ditto 39 18 15


Mean 39 42 12

Mr Kendal's watch made 38 41 30

which is nearly the same difference as the day before. But Mr Wales and I took each of us six distances of the sun and moon, with the telescopes fixed to our sextants, which brought out the longitude nearly the same as the watch.

The results were as follows:--By Mr Wales, 38° 35' 30", and by me, 38° 36'


It is impossible for me to say whether these or the former are the nearest to the truth; nor can I assign any probable reason for so great a disagreement. We certainly can observe with greater accuracy through the telescope, than with the common sight, when the ship is sufficiently steady. The use of the telescope is found difficult at first, but a little practice will make it familiar. By the assistance of the watch, we shall be able to discover the greatest error this method of observing the longitude at sea is liable to; which at the greatest does not exceed a degree and a half, and in general will be found to be much less. Such is the improvement navigation has received by the astronomers and mathematical instrument-makers of this age; by the former from the valuable tables they have communicated to the public, under the direction of the Board of Longitude, and contained in the astronomical ephemeris; and by the latter, from the great accuracy they observe in making instruments, without which the tables would, in a great measure, lose their effect. The preceding observations were made by four different sextants, of different workmen. Mine was by Mr Bird; one of Mr Wales's by Mr Dollond; the other and Mr Clerke's by Mr Ramsden; as also Mr Gilbert's and Smith's, who observed with the same instrument.


The calm was succeeded by a wind from the south; between which point and the N.W., it continued for the six succeeding days, but never blew strong. It was, however, attended with a great hollow swell from the S.W. and W., a sure indication that no large land was near in those directions. We now steered east, inclining to the south, and on the 10th, in the latitude of 43° 39', longitude 144° 43' W., the variation was found, by several azimuths, to be more than 3° E., but the next morning it was found to be 4° 5' 30", and in the afternoon, 5° 56' E. The same day, at noon, we were in the latitude of 43° 44', longitude 141° 56' W.

At nine o'clock in the morning of the 12th, the longitude was observed as follows, viz.

Self 1st set 139° 47' 15"

Ditto, 2d set 140 7 30

Mr Wales 1st set 141 22 15

Mr Wales 2d set 140 10 0

Mr Clerke 140 56 45

Mr Gilbert 140 2 0


Mean 140 24 17-1/2 West.

This differed from my reckoning only 2° 1/2. The next morning, in the latitude of 43° 3', longitude 139° 20' W., we had several lunar observations, which were consonant to those made the day before, allowing for the ship's run in the time. In the afternoon we had, for a few hours, variable light airs next to a calm; after which we got a wind from the N.E., blowing fresh and in squalls, attended with dark gloomy weather, and some rain.

Sidst opdateret:  20:29 23/09 2014

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