New Zealand's first gauge-based sea level measurements

Abstract. James Cook's second voyage to the South Seas, undertaken to settle the question regarding the existence or otherwise of the “Great Southern Continent” (Terra Australis Incognita), involved two vessels, the Resolution and Adventure. The Board of Longitude appointed two astronomers from the Royal Observatory, Greenwich, to the voyage, William Wales and William Bayly, respectively, one to each vessel. They were instructed, in addition to their astronomical duties, to observe the height and time of the tides. To this end, Bayly and Wales fabricated tide gauges and conducted timed measurements of sea level during their stopovers in New Zealand during 1773. This paper reviews those tidal observations, the first of their kind in New Zealand, using modern understanding of the tide, assuming that no significant change in the tidal regime at each location has taken place during the intervening period. When compared to the predicted (hindcast) astronomical tide, the majority (80 %) of the observed ranges and times agreed within 20 cm and 30 min, respectively. Whilst their observations have little scientific value today (other than indicating the quality attainable in the late 18th century), Bayly and Wales can not only rightfully lay claim to making New Zealand's first tide gauge measurements but also, as far as it possible to ascertain, be justifiably proud of the quality of their endeavours.