To have laid down no more than the lands and dangers seen in the Investigator and other vessels under my command, would have left several open spaces, and obliged the seaman to have recourse to other charts where the difference of positions might have perplexed; the discoveries and examinations of former navigators which come within the sphere of each sheet, are therefore incorporated with, or added to mine, but so marked as to be distinctly known. In making the combination, alterations in their longitudes were frequently necessary to agreement; and that they might be made with every regard to accuracy, the charts of the former discoveries were compared with the astronomical observations, narratives, or manuscript journals, when such could be had, and the alterations introduced where there seemed to be the best authority. This has been done with the charts of the east coast of New South Wales, published by Mr. Dalrymple from the manuscripts, as it should appear, of captain Cook; and since it may be thought presumptuous in me to have made alterations in any work of so great a master, this case is selected for a more particular explanation. Time keepers were in their infancy in 1768, when captain Cook sailed upon his first voyage, and he was not then furnished with them; his longitude was therefore regulated only by occasional observations of lunar distances and some few of Jupiter's satellites, which even in the present improved state of instruments and tables, require to be connected by time keepers before satisfactory conclusions can be drawn. Errors of greater or less magnitude were thence unavoidable; at Cape Gloucester, where I quitted the East Coast, my longitude was 20½' greater than captain Cook's chart--at Cape York where the survey was again resumed, it was 58½; and to incorporate the intermediate parts, it was necessary not only to carry his scale of longitude 20½' more west, but also to reduce the extent of the coast. The chart was compared with the narrative and chart in Hawkesworth, and the log book of the Endeavour with them all; when it was found that reductions might be made in various places upon one or more of the above authorities, for differences between them were frequent and sometimes considerable, and in one instance alone a reduction of 12' in the chart was obtained. It is said in Hawkesworth (III, 202), "As soon as we got within side the reef (through Providential Channel) we anchored in nineteen fathom;" and afterwards (p. 204), that the channel, "bore E. N. E. distant ten or twelve miles." In the first chart the distance is 14½ miles, and nearly the same in that which accompanies the narrative; but in the log book it is said to be 2½ miles only, which corresponds with having anchored as soon as they got within the reef, and has been adopted. In some cases it was not easy to make a choice between these different authorities; but I have commonly followed the narrative and log