Shakespeare Head and Cook’s Bay, Mercury Bay with HMS Endeavour
This engraving by an unknown artist appeared in “The Early History of New Zealand” by R.A.A. Sherrin & J.H. Wallace. Brett’s historical series edited by T.W. Leys, 1890
The actual site in the picture is Maramaratotara Bay, commonly known today as Flaxmill Bay.
On Cook’s first voyage, science ruled supreme, for the primary function of the voyage was to accurately observe a transit of Venus from Tahiti. Observations from there were thought to offer the most effective means of determining that basic celestial yardstick, the Astronomical Unit (or AU), which is the distance from the Earth to the Sun.
Although the stated reason for the first voyage was to observe the 1769 transit of Venus, Cook’s ‘sealed orders’ revealed a secondary and, from a political perspective, even more important rationale: i.e. to search for (and if found to claim for Britain) the mooted ‘Great Southern Continent’.
An ex-collier refurbished and renamed Endeavour was chosen for the voyage, as were two astronomers: Lieutenant James Cook and Charles Green. Cook, born 1728, was a career seaman with a solid background in nautical astronomy and coastal mapping. In 1766 he had observed a solar eclipse from Newfoundland. Green was six years Cook’s junior and a former assistant at the Royal Observatory Greenwich. He had observed the 1761 transit of Venus, and in 1763 had taken Harrison’s chronometer on a voyage of evaluation to Barbados.
The Royal Society and the Royal Greenwich Observatory were careful to equip Cook and Green with the requisite scientific instruments, namely Gregorian reflecting telescopes; astronomical quadrants; sextants; astronomical, journeyman and alarum clocks; and pocket watches.
The page of Cook’s journal describing the first and second contact of Venus, 1769. Note the black-drop effect that was felt to be responsible for some measure of uncertainty in the timings.
The transit lasted for about six hours, and was also observed at the other two stations. Observations were published in the Philosophical Transactions of the Royal society. The timings that were deemed critical were of the second ingress contact and the first egress contact. Both Cook and Green had problems in accurately establishing these. Cook explains the black-drop effect and its consequences thus:
“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 (i.e.. Atmosphere of Venus) 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 appeared to converge towards the point of contact, but did not quite reach.”
The problem was to decide precisely when Venus ‘broke free’ from the sun’s limb. Even with these timing uncertainties, there is no justification for the claims that the Tahitian observations were a failure as they did indeed produce a meaningful value for the AU.
Cook’s Third Voyage
The two vessels used on the third voyage were the Resolution, and the Discovery under Captain Charles Clerke. Bayly again served as astronomer, this time on the Discovery. No full-time astronomer was assigned to the Resolution; Cook and King were expected to share the associated duties. King (1750-84) was a naval officer who had studied science in France before moving to Oxford.
The astronomical instruments consigned to the third voyage were very similar to those taken on the previous voyage. Significant astronomical events which attracted the astronomers on the third voyage were lunar eclipses on 30 July 1776, 21 July 1777 and 4 November 1778, and partial solar eclipses on 5 July and 30 December 1777. Anderson, the surgeon on the resolution, noted that for several days before the 5 July 1777 solar eclipse:
“A great many spots were seen in that body (the Sun) which changed daily their number, magnitude and situation, but amongst others there was one place which had a group exactly like a cluster of nine islands.”
Queen Charlotte Sound once more served as a vital stopover centre. By the end of the voyage, the co-ordinates of Ship Cove were known with greater accuracy than almost any other place on Earth!
After the voyage, King and Bayly worked on the official astronomical volume. The resulting volume was eventually published in 1782, and included the late James Cook as an author. However, his surname was somehow spelt incorrectly!
Content taken from James Cook University website. Click here to read more
