The Opening Campaign.

Unless we are deceived by the indications, the country may within a very few days look for the opening of a grand offensive campaign against the rebels. The disposition of our forces is about completed along the entire line, and Lieut. Gen. Grant, as the dispatches have informed us, left Washington for the front on Thursday. A general advance of our armies from the Atlantic to the Mississippi, simultaneously and in co-operation, is confidently expected. The army of the Potomac is under the eye of Gen. Grant in person. Gen. Burnside is in charge of an expedition from Annapolis. Gen. Butler, at Newport News, will move up the Peninsula, while Gen. Sherman at Chattanooga and McPherson at Huntsville are ready to push on our victorious column from the west.

If fortune favors us, it is evident that the rebels with their communications broken through Georgia and Alabama, will ere long be hemmed in around Richmond, and will, by consequence, be compelled to abandon that position. Our dispatches report that Gen. Longstreet has left the region of Knoxville with his forces and formed a junction with Gen. Lee below Culpepper, but we have every reason to believe that the Army of the Potomac is much larger than that of the rebels in its front, while we are sure the advantage of generalship is now on our side.

We have observed vague hints thrown out in rebel prints that the enemy will not wait to be attacked; but intend speedily to take the initiative by a grand raid with 100,000 men through Pennsylvania, while another column, quite as formidable, will penetrate Kentucky, and rallying the disloyal element there, advance into Ohio, Indiana and Illinois. It is, we presume, from apprehensions of this character, that Governors Brough of Ohio, Curtin of Pennsylvania, Morton of Indiana, and Yates of this State, are now in consultation at Washington with the President, with a view to raising an army of 200,000 six months' men to repel these projected raids; but while we may not divine the intentions of the rebel government, we are firm in the belief that before many days, the rebels will have their hands so full in defending themselves from Generals Grant and Sherman, that they will have no time to attend to anything else.

The curtain will soon raise upon the spring's campaign. We have full faith in the result. With a veteran army in the field of 600,000 as brave and determined men as ever carried musket or faced an enemy, with Generals in command who have proved their prowess on many victorious battle-fields, and with a cause which we think enjoys the smile of a protecting Providence, we predict that the death of the rebellion is now near at hand, and that it will not be many days before the country will rejoice in the glorious news of a great and signal victory for the Union.