Agh, so 1851, not 1852 for the Naturalisation Certificate. It was standard procedure in that era for the Governor to sign Naturalisation Certificates. Governors were appointed by the reigning British Monarch. In 1851 as in previous years, the Governor's role was a very significant one involved in the day to day administrative procedures in what was then all of New South Wales.
So the Naturalisation certificate should give you information about your Henri HART, including his ship of arrival and the purpose of his application to seek naturalisation. Usually this reason would be associated with becoming a British Subject with a view to purchasing land. So between when he arrived and his application for Naturalisation he would not have owned any real estate in any of the British Colonies that covered all of continental Australia, nor Van Diemen's Land, nor New Zealand. But after Naturalisation he would have been eligible to purchase land in any British colony. As he was resident in Melbourne, in 1851, and was marrying in New York in 1853, I am linking the index for outward bound passengers for that era:
http://guides.slv.vic.gov.au/migration/outwardI am still confused though, ..... did your Henri HART apply for a US passport in 1853? or was that for someone else? How have you confirmed/eliminated that sighting?
JM