NEW YORK, Aug. 29. — The Alexandria correspondence of the Tribune states that on Tuesday night the pickets at Manassas Junction were driven in and companies of the 100th Pennsylvania infantry, one company of the Pennsylvania cavalry and some artillery stationed there were surprised and attacked by General Ewell's entire division, numbering from 7,000 to 10,000 infantry and cavalry, with artillery. After a short skirmish the handful of men at the Junction fled, the rebels turning upon them nine of our own guns and keeping up a brisk fire till the Union troops were taken prisoners, a few escaping across Bull Run here at Union Mills. Two regiments of Gen. Cox's division, the 11th and 12th Ohio, under Col. Scammon were stationed, and they immediately advanced to meet the approaching body of rebels. A conflict ensued early in the moring between the Junction and Bull Run, lasting for three hours, when the Union troops, being largely outnumbered and flanked on the right, retired across Bull Run bridge. Here a vigorous attempt was made by Col. Scammon to hold the bridge. At 11 o'clock, two rebel regiments forded the Run above the bridge, when the 12th Ohio charged on them and drove them across the river, with tremendous loss. In this skirmish Capt. D. Panley was wounded slightly. The regiment's loss in killed, wounded and missing, is 35 to 40 men. At 12 o'clock Col. Scammon was obliged to retire, moving along the railroad in the direction of Alexandria. The rebels advanced across Bull Run, and yesterday afternoon their advance cavalry were at Fairfax and Burtis Stations. In taking possession of Manassas Junction, the rebels captured seven trains loaded wagons, with provisions, ammunition, &c., and 11 locomotives, all of which they destroyed. Of the eighty-four men of the 105th Pennsylvania on the ground, nearly all were killed, wounded or taken' prisoners, as only three are known to have escaped. Our loss has been immense in government stores, large in killed, wounded, and missing. Telegraphic communication with Gen. Pope was had yesterday, via Fredericksburg. None whatever direct.
Later. — A captain just in from Centerville says that firing was heard early this morning beyond Manassas, and it is believed that Gen. Pope had attacked Gen. Ewell in the rear.
A Washington correspondent states that the 1st New Jersey brigade, Gen. Kearney, is reported to have engaged the enemy near Bull Run bridge, where a desperate struggle was maintained. The bridge is said to be still in our possession. The fighting also was carried on with portions of the division of Gen. Sturgiss. Nine pieces of cannon are said to have been captured by the rebels.
As this goes to mail I learn that telegraphic communication is again opened with Gen. Pope. Manassas, therefore, must be clear of the rebels, and Gen. Stewart, if not taken, is probably wending his way through the Blue Ridge to join the main body of his army. Other correspondents of different papers give similar statements. Nothing can be learned at the war department.