GENERAL GORDON ON BULL RUN.

Sever 11 was filled to overflowing last night with one of the largest audiences that have ever assembled in the room. The occasion was the first of the series of nine lectures on the "Campaigns of the Civil War," its special subject being the second battle of Bull Run. This battle grew out of Gen. Pope's failure to occupy the Confederate armies under Gen. Jackson and Gen. Longstreet, until the army of the Potomac, then operating about Richmond, could meet Lee's army. Gen. Gordon began his lecture by describing the strategic movement of "Stonewall" Jackson from his position on the south bank of the Rappahannock to northward and eastward to Manassas Junction, thereby cutting off Pope's communications from his base of supplies. This took place on the 25th and 26th of August, and was a movement of wonderful brilliancy and rapidity. General Gordon spoke here in the highest terms of Gen. Jackson, as standing pre-eminent in a class at West Point-the class of 1842-which included McClellan, Reno, and A. P. Hill.

The lecturer then proceeded to detail Pope's utterly inefficient policy generally based on his entire ignorance of Jackson's movements. Pope proceeded up the line of the railroad towards Manassas, and gave general orders with a view of massing all the Federal forces at that point or at Centerville, at one of which places he was confident of finding Jackson whom he expected to overpower. By this policy he left the way entirely clear for Jackson to retreat westward and unite with Long street without opposition.

Gen. Gordon gave a complete indication of the conduct of Gen. Fitz John Porter. When Pope advanced westward in pursuit of what he thought was the retreating enemy, he suddenly found himself confronted by Jackson's force. Pope was utterly ignorant of the fact that Longstreet had united with Jackson and now the right wing of the Confederate army. Pope's order to Porter to advance and attack the flank of the enemy, "who are now in the woods before us," was given in utter ignorance of Longstreet's position. To obey Pope's order, Porter would have been obliged, with his ten thousand men, to overcome Longstreet's twenty-five thousand. On the other hand, by holding his position, he kept Longstreet in check and prevented his attacking Pope's flank. In brief, Gen. Gordon showed that Porter's action not only failed to disconcert Pope's plans, but positively helped him. Gen. Gordon illustrated his lecture with maps and plans, and at the close was greeted with great applause.