The purpose of this fourth voyage was clear. A century of exploration had established that a great land mass, North and South America, lay between Europe and the Indies. One by one, the openings in the coast that promised a passage through had been explored and discarded. In fact, Hudson's sail up the Great North River had disposed of one of the last hopes.

But there remained one mysterious, unexplored gap, far to the north. Nearly twenty-five years before, Captain John Davis had noted, as he sailed near the Arctic Circle, ``a very great gulf, the water whirling and roaring, as it were the meeting of tides.'' He named this opening, between Baffin Island and Labrador, the ``Furious Overfall.'' (Later, it was to be called Hudson Strait.)

In 1602, George Waymouth, in the same little Discovery that Hudson now commanded, had sailed 300 miles up the strait before his frightened men turned the ship back. Hudson now proposed to sail all the way through and test the seas beyond for the long sought waterway.

Even Hudson, experienced in Arctic sailing and determined as he was, must have had qualms as he slid down the Thames. Ahead were perilous, ice filled waters. On previous voyages, it had been in precisely such dangerous situations that he had failed as a leader and captain. On the second voyage, he had turned back at the frozen island of Novaya Zemlya and meekly given the crew a certificate stating that he did so of his own free will -- which was obviously not the case. On the third voyage, a near mutiny rising from a quarrel between Dutch and English crew members on the Half Moon had almost forced him to head the ship back to Amsterdam in mid Atlantic.