Sydney's Scientific Beginnings: William Dawes' Observatories in Context.

The voyage of the "First Fleet" from Britain to the new colony of New South Wales was not only a military enterprise, it also had a distinct scientific purpose. Britain's fifth Astronomer Royal, Nevil Maskelyne, had selected William Dawes, a promising young Marine with a propensity for astronomical observations, as his prot\'eg\'e. Maskelyne convinced the British Board of Longitude to supply Dawes with a suite of state-of-the-art instruments and allow the young Marine to establish an observatory in the new settlement. The Astronomer Royal may have had a dual motivation, one driven by strategic national interests combined with a personal investment linked to the suggested re-appearance of a comet in the southern sky. With the unexpected assistance of the French Lap\'erouse expedition, between 1788 and 1791 Dawes established not one but two observatories within a kilometre of Sydney's present-day city centre. Motivated by persisting confusion in the literature, we explore the historical record to narrow down the precise location of Dawes' observatory. We conclude that the memorial plaque attached to Sydney Harbour Bridge indicates an incorrect location. Overwhelming contemporary evidence -- maps, charts and pictorial representations -- implies that Dawes' observatory was located on the northeastern tip of the promontory presently known as The Rocks (formerly Dawes' Point), with any remains having vanished during the construction of the Harbour Bridge.