Time makes many dark things clear, and often in a wonderfully short and decisive way. So we said hopefully two years and more ago in regard to one of the unsolved problems which then pressed on the minds of thoughtful men--how, namely, it was to fare with slavery in the progress and sequel of the war. The history of our national struggle has illustrated the truth and justified the hope. Time has quite nearly solved that problem and some others almost equally perplexing. The stream of historical causes has borne the nation onward on the bosom of its inevitable flow, until we can now almost see clear through to the end; at any rate, we have reached a point where we can look backward and forward with perhaps greater advantage than at any former period. What changes of opinion have been wrought! How many doubts resolved! How many fears dispelled! How many old prejudices and preconceived notions have been abandoned! How many vexed questions put at rest! How many things have safely got an established place among accepted and almost generally acceptable facts, which were once matters of loyal foreboding and of disloyal denunciation! No man of good sense and loyalty now doubts the rightfulness and wisdom of depriving the rebels of the aid derived from their slaves, and making them an element of strength on our side; while the fact that the enfranchised slaves make good soldiers, is put beyond question by an amenability to military discipline and a bravery in battle not surpassed by any troops in the world. HAS THE WAR GONE SLOWLY? The work of subduing the rebellion has gone slowly as compared with the impatient demands of an indignant people at the outset; but not slowly if you consider the vast theatre of the war, the immense extent of the lines of military operations, and the prodigious advantages possessed by the rebels at the beginning--partly advantages such as always attend the first outbreak of a revolutionary conspiracy long matured in secret against an unsuspecting and unprepared Government, and partly the extraordinary and peculiar advantages that accrued to them from the traitorous complicity of Buchanan's Administration, through which the conspirators were enabled to rob the national treasury, strip the Government of arms, and possess themselves of national forts, arsenals, and munitions of war, before the conflict began. NOT TOO SLOW--WHY? SLAVERY.