Lord NELSON sailed from St. Helen's in the Victory, with the Euryalus frigate, on the morning of the 15th of September 1805, to take the command of the British Fleet cruizing before Cadiz. On the 18th he appeared off Plymouth; where he was joined by his Majesty's ships Thunderer and Ajax, with which he proceeded for his destined station. On the 20th he communicated by private signal with the squadron under the command of Rear-Admiral STIRLING, which passed within a few miles of the Victory; and the same day at noon, spoke his Majesty's ship Le Decade, having on board Rear-Admiral Sir RICHARD BICKERTON, who,.