On Cook's return from his second voyage he received, from the hands of King George III, his commission as a post captain in the navy, and soon afterwards was appointed to be a fourth captain at the Royal Hospital for Seamen at Greenwich, with a salary of £200 a year, a residence, and certain allowances, subject, however, to the right of the Admiralty to call on him for further sea service should they require him. And the call—provoked by the eagerness of Cook—was not long delayed, for in the following year (1776) he was appointed to command once more the Resolution. To this ship was added a smaller consort, the Discovery, which had a capacity of only 300 tons, to be commanded by Lieutenant Clerke, formerly of the Resolution.

In the Third Voyage, which began in the summer of 1776, the exploration of the Pacific was to be continued, but more with the intention that Cook should explore the western coast of North America and find out conclusively if there was or was not any sea way which would give a passage for ships across the North American continent.[104] The new voyage to be undertaken by the ships Resolution and Discovery was designed to proceed to the Pacific by the Cape of Good Hope across the Indian Ocean in southern latitudes, and past New Zealand and Tahiti to the west coast of North America. Rumours had begun to reach England about French discoveries in the South Indian Ocean, notably those by du Fresne and Crozet and by de Kerguélen-Trémarec in 1772, which it was desirable to investigate. An interesting member of Cook's crew was a Tahitian—Omai—who had been brought to England by the Adventure, and had not been spoilt by the kindliness of his reception. Omai was to return with Cook to his native land, and proved himself as useful, plucky, good-natured, and well-mannered an interpreter as had done the unfortunate Tupia, whose bones lay buried at Batavia. After the usual stay at the Cape of Good Hope, the Resolution and Discovery made their way into the Southern Indian Ocean through mountainous seas and bitter cold weather, and discovered or rediscovered Prince Edward's Island,[105] the Marion du Fresne and the Crozet Islands, and came to an anchor off the large island in 48° S. latitude, which had been already noted by the French sea captain, de Kerguélen-Trémarec. This last-mentioned island now bears Kerguélen's name. Captain Cook and the great French explorers who had preceded him had found no vast southern continent in the Southern Indian Ocean, but all unknowing they had found the last remaining vestiges of such; for Kerguélen, St. Paul, and Amsterdam Islands, the Crozets and Prince Edward's Islands, are the only portions remaining above the sea of a great Antarctic land which probably once united South America with Australia and New Zealand. All these scattered oceanic islands rise from what is called the Kerguélen Plateau, a region of the bed of the Indian Ocean in which the depth does not much exceed 8000 feet.

Kerguélen is the largest of these islands—about 1400 square miles in extent. Its mountains attain altitudes of 2400 to 6120 feet. One of them is an active volcano, and the whole of Kerguélen has been subjected in recent times to much volcanic activity, lava having covered much of its surface. This eruption of plutonic forces seems to have followed a severe glacial period, during which the island was covered with ice. It is therefore not to be wondered at that between them fire and ice destroyed a once abundant plant growth; for Kerguélen, in Tertiary times, maintained great forests of trees of South American affinities.

On this desolate wind-swept island of snow mountains and crumbling lava the crews of the Resolution and Discovery spent Christmas, partly to obtain fresh water ("every gully afforded a large stream") and fresh meat—the flesh of penguins and other sea birds and seals. The seals (chiefly sea elephants and sea leopards) also provided quantities of fat or blubber, from which oil was obtained for the ship's lamps. The principal feature in the vegetation (there were no trees, except fossil ones) was a plant called the Kerguélen cabbage, actually a kind of cabbage (Pringlea antiscorbutica). This was a great boon to the ship's company, who ate it boiled and also raw in their eagerness for vegetable food. Amongst the birds of the island was a land bird, the sheathbill (Chionis), the size of a large pigeon, with white plumage, black beak, and white feet, a bird which is related both to the gulls and the plovers. There were also giant petrels, king penguins, albatrosses, gulls, cormorant and a peculiar species of teal.

On 24 January, 1777, the coast of Tasmania was sighted, and on the 27th the second party of Englishmen (the men of the Adventure being the first) landed in that southernmost portion of Australia. The following day a party of natives appeared, who approached them unarmed without betraying fear. They were quite naked and wore no ornaments, but their bodies were decorated by large weals or ridges of skin in straight or curved lines. They were of average size, rather slender, with black skins and black woolly hair. Their features were not ugly. The language was wholly unintelligible, and seemed even to be different from that of the natives of New South Wales.

After a further visit to New Zealand, and a long stay in the Friendly Islands (the Tonga archipelago) and the Society Islands, Cook turned the course of his expedition northwards, discovered Christmas Island, and sailed across a stretch of open ocean till at last, in January, 1778, he sighted a wonderful new land in the archipelago of Hawaii. To this he gave the name by which they were long afterwards known—the Sandwich Islands. After a stay in this region of eight principal islands and many islets, with its wonderful volcanoes (the highest of which is snow-crowned and 13,823 feet in altitude), its peculiar vegetation, and its Polynesian people, he passed on to the exploring of the western and north-western coasts of North America, with the results which have been described in my book on the Pioneers in Canada. Returning again southwards to continue the explorations of the Pacific archipelagos, he met his fate in a miserable skirmish on the west coast of the large island of Hawaii, the easternmost of the Hawaii group.[106]

Cook's adventures and those of his officers, after reaching northern latitudes such as the Hawaii archipelago, can scarcely be brought within the limits of Australasia, so that Cook now passes from our narrative. But he remains the most remarkable figure in the past history of Australasia. He was perhaps the greatest of British navigators, for he made not only all the most remarkable discoveries of the Pacific Ocean between the ice fringe of the Southern Continent and the Bering Straits; but he did so with singularly little hardship to his men, whose health he studied with the utmost care, while in his contact with the natives he has left behind him an admirable reputation for kindliness and sympathy. From the point of view of science he fully deserved the Fellowship of the Royal Society. The books composed from his journals read like those of modern travellers of the best type, so shrewd are his observations and so accurate his descriptions. He stands in the first rank of the world's heroes, and it is interesting to remember that, though there are not many greater Englishmen in our national records, he rose from being the son of a Yorkshire farm labourer, a boy serving out groceries in a little shop, an apprentice on board a collier, to command, as an officer in the king's navy, vessels which performed voyages far more wonderful than that of Columbus, and which revealed to the knowledge of science the coasts of the Arctic and Antarctic Oceans, the Continent of Australia, the Dominion of New Zealand, and most of the islands and archipelagos of the Pacific Ocean.