During the week we remained in Caledon Bay, the following astronomical observations were taken.
Latitude from three observations to the north and south, taken in a boat astern of the ship and reduced to the tents on Point Alexander, 12° 47' 16" S.
Longitude from twelve sets of distances of stars east and west of the moon, taken on a stand by lieut. Flinders, and of which the individual results are given in Table VI. of the Appendix No. I, 136° 35' 47.5" E.
The rates of the time keepers were found from morning's altitudes of the sun in an artificial horizon, between Feb. 3 and 8; and the means, with the errors from mean Greenwich time at noon there on the 9th, were as under:
Earnshaw's No. 543, slow 2h 41' 0.91" and losing 16.53" per day. Earnshaw's No. 520, slow 2h 27' 19.55" and losing 30.83" per day.
No. 520 had been accidentally let down in Blue-mud Bay, whence its longitude is not now noticed; that given by No. 543 on Feb. 3, with the rate from Observation Island, was 136° 43' 3.5", or 7'16" greater than the lunars. Were a rate used, equally accelerated from that of Observation Island to what was found in Caledon Bay, the longitude would be 0' 55" less than the lunars; but during the twelve days occupied in circumnavigating Groote Eylandt, it was proved that this time keeper was keeping its former rate, and consequently the acceleration cannot here be admitted.
In constructing the chart of the coast and islands between Pellew's Group and Caledon Bay, a time keeper was required only in laying down the south and east sides of Groote Eylandt, and the main coast up to Cape Barrow; in all the remaining parts the longitude was preserved by a connected chain of bearings, mostly taken on shore. The time-keeper reckoning from Observation Island, and that by survey worked back from the fixed point in Caledon Bay, meet each other on Jan. 5 p.m. at Connexion Island; and the difference was there found to be 2' 41", which the time keeper gave more to the east. This may have arisen from Observation Island being laid down in a longitude too great by that quantity, or Caledon Bay too little, or from a small error in each; but the time keeper was not thought entitled to such perfect confidence, as to cause an alteration to be made in these stations. The difference of 2' 41" is therefore corrected by applying -16.3" of longitude per day to the time keeper, from Observation to Connexion Island; Groote Eylandt is laid down mostly from the time keeper, with the fixed correction -2' 41" all round; and from thence to Caledon Bay the chart is constructed from bearings and observed latitudes.
The mean dip of the south end of the needle, observed at the tents, was 36° 28'.
Variation of the theodolite, 2° 20' E.
On board the ship, at anchor off the south-west side of the inner island at the entrance, the variation from three compasses, with the head N. W. by W., was 2° 26'; by the surveying compass alone, 2° 46' east, and this, which I consider to be the best, would be, corrected, 1° 14' E.