The main bodies of the contending navies did not come in sight of each other during the 20th; the British lookout frigates, between the two, and three or four miles from the allied line, could see their own fleet only from the masthead.  At about 2 P.M., soon after the weather cleared, the wind shifted to west-northwest, taking the ships aback.  After filling their sails again to the new wind, as this was now fair for their approach to the Straits’ mouth, the combined fleets wore, and headed to the southward.  The British remaining on the same tack as before,—­the port,—­stood to the northward until 8 P.M., when they also wore to the southwest; but this interval of steering in nearly opposite directions changed the relative bearings.  At midnight, by the log of Blackwood’s frigates, the enemy stretched along the eastern horizon, while the British bore southwest; the space between the two being ten miles.  The “Euryalus,” three miles from the allies, saw the loom of the lights of her own fleet.  Still fearful lest the view of his ships should shake the enemy’s purpose, Nelson was careful not to lessen this distance; the more so because the British, having the wind, could attack when they pleased, provided the enemy by continuing to the southward deprived themselves of the power to regain Cadiz.  Two British frigates were directed to keep them in sight during the night, reporting their movements to two others who were stationed a little farther from them, whence a chain of line-of-battle ships communicated with the “Victory.”  Thus, throughout the dark hours, signal lights and guns flashed across the waters to Nelson instantaneous information of every noteworthy occurrence in the hostile order.

Since the morning of the 19th, the weather, fine for some days previous, had become unsettled, working up for the southwest gale which wrought so much damage among the victims of the fight.  As the night of the 20th advanced, the wind fell, and at midnight there were only light westerly breezes, inclining to calm.  The same conditions continued at dawn, and throughout the day of the 21st until after the battle; but there was also a great swell from the westward, the precursor of a storm.  At 4 A.M. the British fleet again wore, and was standing northeast when the day broke.

After leaving Cadiz, in order to avoid separations during the night, or in thick weather, the combined fleets had been disposed in five columns, a formation whose compactness, though not suited to an engagement, was less liable to straggling than a single long line, and brought all parts more directly under the control of the commander-in-chief at the centre.  Of the five, the two to windward, of six ships each, constituted a reserve, similar to Nelson’s proposed detachment of eight.  It was commanded by Admiral Gravina, and was intended to reinforce such part of the battle as should appear to require it; an object for which the windward position was of the utmost moment, as it was for all naval initiative in that day.  This advantage the allies did not have on the morning of Trafalgar.  When Villeneuve, therefore, formed the line of battle, these twelve ships were at once incorporated with it, taking the lead of their order as it stood to the southward, with the wind at west-northwest,—­a long column stretching over five miles of sea from end to end.