Andrew David - Hydrographer and Hydrographic Historian, United Kingdom, Discussing chart making and longitude
There were two main instruments. One was the development of the sextant in the early part of that century. And then of course there was the development of the chronometer, both of which were essential for obtaining longitude. Prior to Cook's first voyage, you couldn't obtain your longitude in the Pacific, or anywhere, with any accuracy. The Solomon Islands, for many years, were thousands of miles out of position in longitude, and it was only until the advent of the chronometer that their position was found accurately.