The Great battle of Gettysburg is now an event of the past. The composition and strength of the armies, their leaders, the strategy, the tactics, the result, of that field are to-day by the side of those of Waterloo—matters of history. A few days ago these things were otherwise. This great event did not so "cast its shadow before," as to moderate the hot sunshine that streamed upon our preceding march, or to relieve our minds of all apprehension of the result of the second great Rebel invasion of the soil North of the Potomac...