Page:A Voyage to Terra Australis Volume 1.djvu/9

Rh 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,