Féth Fíada, or the druid's fog, is thought to be an enchantment. The fog conceals someone, makes them invisible, and fog can truly do that anyway, right?
There are two kinds of mist or fog in Ireland, one of which is constant and uniform, filling the whole air in such a manner as to impede the view, and continuing in the same state till it vanishes, either by rising into the atmosphere or falling to the earth. This kind is commonly followed by rain.The other consists of clouds of foggy vapours, scattered about, with clear spaces between them. These clouds are often strongly agitated, and sometimes driven about with great velocity. This species of fog arises, not only on the sea coast, but also in the interior of the country upon mountains, and often terminates in one general mist.
On August 28, severe rain storms prevented any fighting between Washington and Howe. Both sides stayed in place. Also, because of the high winds, Howe was unable to move his warships behind Washington's position.
On August 29, during the evening, Washington called a council-of-war to consult on the proper measures to be taken. It was determined that moving across the river was the only way to escape. Washington ordered that all boats that could be found to be gathered up. The plan was to use the boats to ferry his troops across the river to safety. This way, they could escape the British trap and withdraw undetected from Brooklyn Heights. A heavy rain and fog kept the patriot escape from being seen from Howe. Heavy winds continued to keep the British ships from advancing to Washington's position.
The withdrawal started soon after it was dark from two points, the upper and lower ferries, on the East River. The intention of evacuating the island had been so prudently concealed from the troops that they did not know where they were going. The field artillery, tents, baggage, and about 9,000 men were conveyed over East River, more than a mile wide, in less than 13 hours. Being only 600 yards away, Howe and the British army had no knowledge of the Patriot withdrawal that was proceeding.
On August 30, around 6:00 A.M., the last of the Patriots left the shore of Long island. The withdrawal had worked without the british finding out.
At 11:00 A.M., the heavy winds finally died down enough for the British warships to begin to move upriver.
At 11:30 A.M., the fog lifted. Howe ordered his troops to advance and take the Patriot works. When they arrived, they discovered that the Patriots were nowhere to be seen. Howe realized that he had let Washington and the Patriots slip through his grasp. The British warships were finally able to move upriver, just a few hours too late to stop the Patriots. If Howe could have captured Washington and his troops, this would have effectively ended the war.
So, the Féth Fíada was carried on in colonial America, it seems!