In 1797, in an open whaleboat with a crew of six, Bass sailed - or rather rowed - to Cape Howe, the farthest point of south-eastern Australia. From here he went westwards along what is now the coast of the Gippsland region of Victoria, almost as far as the site of present-day Melbourne. His belief that a strait separated the mainland fron Van Diemen's Land (now Tasmania) was backed up by his astute observation of the rapid tide and the long south-western swell at Wilson's Promontory.
In 1798, this theory was confirmed when Bass and Flinders, in the sloop Norfolk, circumnavigated Van Diemen's Land. In the course of this voyage Bass found and explored the estuary of the Derwent River, where the city of Hobart would be founded, on the strength of his report, in 1803. When the two returned to Sydney, Flinders recommended to Governor John Hunter that the passage between Van Diemen's Land and the mainland be called Bass Strait.
"This was no more than a just tribute to my worthy friend and companion," Flinders wrote, "for the extreme dangers and fatigues he had undergone, in first entering it in a whaleboat, and to the correct judgement he had formed, from various indications, of the existence of a wide opening between Van Diemen's Land and New South Wales."
Bass was an enthusiatic naturalist and botanist, and he forwarded some his botanical discoveries to Sir Joseph Banks in London. "In this voyage of fourteen weeks I collected those few plants upon Van Diemen's Land which had not been familiar to me in New South Wales," he wrote to Banks, "and have done myself the honour of submitting them to your inspection." He was made an honorary member of the Society for Promoting Natural History, which later became the Linnean Society. Some of his observations were published in the second volume of David Collins's An Account of the English colony in New South Wales. He was one of the first to describe that loveable Australian marsupial, the wombat.
Bass returned to England in 1799, and married Elizabeth Waterhouse. Restless, he went to sea again in 1801, and sailed to Sydney on a cargo vessel. After engaging in some business in Sydney, he sailed on a commercial venture to Tahiti in February 1803 on the brig Harrington. He was never heard of again. It is most likely that the ship was lost at sea, although it is possible that it was captured in the eastern Pacific by the Spaniards.