Observations made, by appointment of the Royal Society, at King George’s Island in the South Seas

From Wikisource
Jump to navigation Jump to search
Observations made, by appointment of the Royal Society, at King George’s Island in the South Seas  (1771) 
Mr. Charles Green, formerly Assistant of the Royal Observatory at Greenwich, and Lieut. James Cook,* of His Majesty's Ship the Endeavour

Read to the Royal Society (of London) in 1771, and published in the transactions of the same (p. 397.) spanning 25 journal pages including contact drawings by Cook and Green. The text here is reproduced from C. Hutton, G. Shaw and R. Pearson, The Philosophical Transactions of the Royal Society of London, from their Commencement, in 1665, to the Year 1800; abridged, with Notes and Biographic Illustrations..(London: C. and R. Baldwin, 1809), XIII, pp. 173-78.[1][2][3]

This gentleman was Capt. James Cook, the celebrated circumnavigator, who made, by authority, three voyages round the earth; in the last of which he was killed by the natives of one of the Sandwich Islands, the 14th of Feb., 1779, at 51 years of age. An ample account of the life of this extraordinary man is given in the Biographia Britannica. The following are a few particulars of him. He was born at Marton, in Yorkshire, in 1728, of parents in humble circumstances; and at an early age he was apprenticed to a shopkeeper at Snaith; but afterwards bound himself to a ship owner in the coal trade at Whitby, in which line he served many years. But, on the breaking out of the war in 1755, he entered on board a man of war; where distinguishing himself, by his good conduct, in 1759 he obtained a master's warrant. In that capacity he served at the reduction of Quebec, where he took the soundings of the river St. Laurence, and made an accurate chart of it. He next served at the retaking of Newfoundland, where also he made a survey of the coast, with other curious researches, and observed there an eclipse of the sun, Aug. 5, 1766, printed in the Philos. Trans., vol. 57. In 1768, with the rank of lieutenant, he was appointed to the command of the Endeavour, accompanied by Mr. Green, astronomer, to observe the transit of Venus at Otaheite, in the South Seas; and an account of their observations on that occasion is given in the article above. Along with them also sailed Mr., now Sir Joseph Banks, and Dr. Solander. After the transit was discovered, Mr. Cook sailed on a voyage of discovery, in which he discovered and visited a number of new lands; as the Society Islands, New Zealand, Nevis Holland, Botany Bay, &c. In June, 17, 1771, he arrived in England, and was appointed a commander in the navy, an account of the voyage being published by Dr. Hawksworth.

In 1772 he was again sent out on another voyage, with two ships, the Resolution, commanded by himself, and the Adventure, by Capt. Furneaux. In this voyage he explored the southern hemisphere as far as latitude 71° 10', amidst immense fields and mountains of ice. Capt. Cook then touched at Otaheite to refresh, and hence sailed to the westward, and visited several groups of islands; as, what he called the Friendly Isles, also the islands discovered by Quiros, called by Capt. C. the New Hebrides; also New Caledonia, and Norfolk Island, which has since been colonized. After many other additions to our geographical knowledge, but without attaining the main object, the discovery of a southern continent, he arrived in England, July 1775, having lost only one man, out of 118 on board his ship,owing to the excellent means he employed for preserving the health of the crew. Of these means he gave an account in a paper sent lo the R. S., where he was chosen a member of their body, and his paper honoured with the prize medal in 1776. He was also, by the Government, raised to the rank of a post captain in the navy, and appointed to an office in Greenwich Hospital; and an account of his voyage was drawn up by himself and Mr. Wales.

The government having resolved to ascertain whether there be a northern communication between the Atlantic and Pacific oceans, Capt. C. volunteered his services on the occasion, and in July 1776, he sailed in the Resolution, accompanied by another vessel. After touching at some of the South Sea islands, he proceeded northwards, and discovered the group which he named the Sandwich Islands; hence proceeding to the northwest coast of America, he traced along all that coast, as far as latitude 74°, where their progress was stopped by an impenetrable mass of ice, extending between the north-east point of Asia and the north-west point of America. Hence he returned to the southward, and in November 1778, he revisited the Sandwich Islands, where he was unfortunately killed in a quarrel with the natives.

Of these observations, the first is a series of equal altitudes of the sun, for the time, made with the astronomical quadrant: from the whole of these it is inferred, hence the daily rate of the clock's losing on mean time, by a mean of 40 results, is 20.8 seconds. By else first and last days observations compared together, the clock lost 19m 49s.9 on mean time in 57 days, which is at the rate of 20s.88 or 20s.9 per day. The swing of the pendulum on each side of the perpendicular during this time, varied between 1° 50' and 1° 55.

Remark.--The same clock, when fixed at the Royal Observatory at Greenwich, before the voyage, with the pendulum of the same length, got at the rate of lm 45.8s per day, on mean time, between April 19 and July 18, 1768. Therefore the force of gravity at Greenwich is to that at King George's Island, as 1000000 to 997075. N. Maskelyne.

Next follows a series of observations of meridian zenith distances of the sun and fixed stars, for finding the latitude of the observatory: from which it is found, that the mean of all the results from the sun and six stars to the North, gives the latitude 17° 28 51"s; and the mean of all the results from the stars to the south, gives the latitude 17° 29' 38" s: the mean of these two means is 7° 29' 154" s. which may be taken for the latitude of the observatory.

Remark.--It must be confessed, that the results of these observations (most of which were made by Mr. Green) differ more from one another than they ought to do, or than those do made by other observers, with quadrants of the same size, and made by the same artist, the cause of which, if not owing to want of care and address in the observer, I don't know how to assign. N. Maskelyne.

The next is a series of lunar observations, that is, of the moon's distances from the sun and stars, for the longitude; the mean from all these give the longitude of the observatory, on George's Island, 149° 36' 38" west of Greenwich observatory. To these succeed a set of observations of the eclipses of Jupiter's satellites, for the same purpose; from which it is inferred that the longitude of the same place is 149° 32' 30".

Next, the observations of the main object, the transit of Venus, is given at considerable length, by the different observers. And,

1st. By Mr. Green, with a reflecting telescope of 2-feet focus, magnifying power 140 times.
Apparent time.
June 2.
Light thus on the Sun's limb, pl. 1 21h 25m 40s
Certain, as in fig. 2 21 25 55
First internal contact of Venus's limb and the Sun, fig 4 21 43 15
Penumbra and Sun's limb in contact, fig. 5 21 43 55
June 3,
First contact of penumbra, undulating, but the thread of light visible and and invisible alternately 3 14 3
Second internal contact of the bodies 3 14 3
Second external contact 3 31 28
Total egress of penumbra, O's limb perfect 3 32 14

2. Transit of Venus by Capt. Cook, with a reflecting telescope of 2 feet focus, and the magnifying power 140.
June 2,
The first visible appearance of Venus on the Sun's limb, see fig. 1 21 25 45
First internal contact, or the limb of Venus seemed to coincide with the Sun's fig. 2 21 43 15
A small thread of light seen below the penumbra, fig.3 21 44 15
June 3,
Second internal contact of the penumbra, or the thread of light wholly broke 3 14 13
Second internal contact of the bodies, and appeared as in the first 3 14 45
Second external contact of the bodies 3 31 22
Total egress of penumbra, dubious 3 32 2

The first appearance of Venus on the sun, was certainly only the penumbra, and the contact of the limbs did not happen till several seconds after, and then it appeared as in fig. the 4th; this appearance was observed both by Mr. Green and me; but the time it happened was not noted by either of us; it appeared to be very difficult to judge precisely of the times that the internal contacts of the body of Venus happened, by reason of the darkness of the penumbra at the sun's limb, it being there nearly, if not quite, as dark as the planet. At this time a faint light, much weaker than the rest of the penumbra, appeared to converge towards the point of contact, but did not quite reach it, see fig. 2. This was seen by myself and the two other observers, and was of great assistance to us in judging of the time of the internal contacts of the dark body of Venus, with the sun's limb. Fig. the 5th is a representation of the appearance of Venus at the middle of the egress and ingress, for the very same phenomenon was observed at both: at the total ingress, the thread of light made its appearance with an uncertainty of several seconds; I judged that the penumnbra was in contact with the sun's limb 10s sooner than the time set down above; in like manner at the egress the thread of light was not broke off or diminished at once, but gradually, with the same uncertainty; the time noted was when the thread of light was wholly broke by the penumbra. At the total egress I found it difficult to distinguish Venus's limb from the penumbra, which of course made the second external contact a little doubtful, and the precise time that the penumbra left the sun could not be observed to any great degree of certainty, at least by me. Some of the other gentlemen, who were sent to observe at different places, saw at the ingress and egress the same phenomenon as we did; though much less distinct, which no doubt was owing to their telescopes being of a less magnifying power; for the penumbra was visible through my telescope during the whole transit; and Dr. Solander, whose telescope magnified more than ours, saw it, I have reason to think, distincter than either Mr. Green or myself; though we both of us saw enough to convince our senses, that such a phenomenon did indisputably exist, and we had a good opportunity to observe it, for every wished for favourable circumstance attended the whole of that day, without one single impediment, excepting the heat, which was intolerable: the thermometer, which hung by the clock, and was exposed to the sun as we were, was one time as high as 119°. The breadth of the penumbra appeared to me, to be nearly equal to 1/8 of Venus's semidiameter.

3. Transit of Venus by Dr. Solander, with a 3-feet reflecting telescope. First external contact plainly convex, a wavering haze seen some seconds before

App. time
Ingress, light seen glimmering under Venus 21h 43m 28s
Venus's free from the Sun's limb 21 44 2
Venu's true limb out 3 31 49
Venus's atmosphere out 3 32 13

4. Observations of the transit of Venus, made by Mr. Charles Green, with Dollond's micrometer fitted to a reflecting telescope of 2-feet focus, gave on the day of the transit, for the diameter of Venus, 54".9, on a medium of the whole, and that of the sun 31' 27".4. At these observations the thermometer stood at 113°.

5. Observations on the transit of Venus, June 3, 1769, by Dollond's micrometer fitted to a reflecting telescope of 18 inches focus, by Capt James Cook. The mean of all these give 56".4 for the diameter of Venus.

Observations on the Dipping Needle.
Time when Place where Dip of the north or south point
September 13 In Funchal Bay, dip pf N. end of needle 77 18'
October 25 Crossing the line in long. 30o 18' w. of Greenwich 26 to 28 N. point
January 10 At sea in lat. 52° 54's. and long. 63° 10' w 63 S. point
January 20 Good Success Bay in Straits Le Maire 68 51 ditto
January 24 On board the ship at anchor in the above bay 65 0 ditto
January 30 Ditto ditto, 60° 4' s. long. 74° 10' w 65 17 ditto
March 3 ditto ditto, 36 49 s. ditto 111 54 w 65 52 ditto
March 13 Ditto ditto, 30 46 s. ditto 125 28 w 64 25 ditto
April 5 Ditto ditto, 18 25 s. ditto 140 51 w 30 0 ditto
May 30 George's island, lat. 17° 29's long. 149° 34' w 30 43 ditto

N. B. Each of the above observations is the mean of 10, 12, or more; with the face of the instrument turned alternately east and west: those made at sea are a little dubious on account of the motion of the ship; but, by means of a swinging table we had made to set the compass on, we could, in a tolerable smooth sea, be certain of the dip to a degree, or at the most 2, by taking the mean of a great number of trials.

Lastly are given a set of observations on the tides at George's Island, by which it is inferred by the astronomer royal, that the mean height of the sides is about 10 inches, and the greatest height scarcely exceeds one foot, in the middle of this wide extended ocean, which falls far short of what might have been expected from physical principles. The cause of this remarkable difference deserves further inquiry. The time of high water also appears to precede the moon's passing the meridian by 45 minutes at a medium, and the time of low water to precede the same, by 6h3lm. But the mean difference of high and low water, should be 6h 12m, which subtracted from 6h 31m, leaves 19m, by which the time of high water should precede the moon's passing the meridian, the mean of this and 45m is 32m, by which the time of high water precedes the moon's passing the meridian, by a medium of all the observations. The times of high and low water seem to be subject to great irregularity on particular days; no doubt owing to the small rise of tile water, and the smallness of its force in consequence, which renders it more liable to be disturbed by the action of the winds and other causes; part of the irregularity may be attributed to the difficulty of observing the time of the flood or ebb, with any degree of certainty. N. Maskelyne.

N. B. The island here named King George's Island, is called by the natives Ota-heite, by which name it will henceforth be called, the name of King George's Island having been given before to another island in lat. 14 s. discovered by Commodore Byron.

* Mr. Green having died at sea in the passage home from Batavia, all the astronomical and other observations were partly arranged by Capt. Cook, and partly by the astronomer royal, from the original manuscripts, and calculated by the latter.

This work was published before January 1, 1927, and is in the public domain worldwide because the author died at least 100 years ago.