GENERAL OPDYCKE'S LECTURE.

Sanders Theatre was last night the scene of a lecture by General Opdycke on the above-named subject. The Historical Society had issued tickets to the floor for its friends, while the general public was admitted to the first gallery. Both these portions of the theatre were crowded, and many asked why admittance to the second gallery was denied. Several who were unable to get seats below wandered up-stairs only to find the doors shut.

When the season for campaigning opened in 1863, the forces of the Union and of the Confederacy were opposing each other in three parts of the South, in Virginia, on the Mississippi, and in Tennessee. It is with the operations in this latter place that the subject treated. Rosecrans commanded the Union army of the Cumberland. Opposed to him was General Bragg, with 50,000 Confederates. The object towards which the army under Rosecrans was moving was Chattanooga. This city, a natural fortress, was situated at the base of the mountains in East Tennessee. Here converged all the railway lines which made the easy movements of troops from one part of the South to another possible. Thus its possession was of vital importance to the Confederacy. Important to them it was the goal which Rosecrans must reach before he could hope to penetrate into the heart of the South. To aid him, General Burnside was moving on Knoxville, a little further north, with Chattanooga as his final aim.

If these two forces should accomplish their object by the capture and permanent possession of this important city the first step toward a great scheme would be accomplished. Then the loyal citizens of eastern Tennessee would be protected, and Kentucky, free from inroads, would be saved to the Union. Moreover, from Chattanooga railways led either north and east to Lynchburg and Richmond in Virginia, or southeasterly to Atlanta. By following either of these routes the Union generals hoped to break up the Confederacy at a single blow. After much delay Rosecrans moved forward and compelled Bragg who was blocking the road and passes to Chattanooga to retire into that city. Rosecrans advanced still farther and by skillful manoeuvering which deceived Bragg placed that general in such a position that he had no alternative but to retreat at once or undergo a blockade and starvation. Bragg, in this unfortunate dilemma, wisely concluded to retreat. He marched away behind the mountains and awaited the movements of his opponent. Rose crans, hitherto successful, now began to make mistakes. He moved forward after Bragg and separated his three corps. This was dangerous, for to hold his long line of communication much of his army had been detached from his active field force. Bragg, on the other hand, had received large reinforcements, among them the celebrated corps of Longstreet from Lee's army in Virginia. These gave him a numerical superiority and he, in his turn, prepared to take the offensive and crush Rosecrans' detached forces. Here was a great opportunity to retrieve the drooping fortunes of the South by one bold move. But Rosecrans could gain little and close much by fighting a superiorforce so far from Nashville, his base of supplies. He would have done better to have waited in Chattanooga until more troops and supplies should put him in a perfectly safe condition.

Bragg's plan of attack on the Union army, most of which was now, Oct. 19th at Chickamauga Creek, was to turn its flank and gain possession of the indispensable road back to Chattanooga. During all of that day there was heavy fighting with but little advantage to either side. This was only preliminary. During the night Rosecrans reposted his army, and in the morning was in a better position to resist attack. This was soon made by Polk on our left, which was commanded by Thomas. Although hotly pressed, the left wing stood firm and Thomas called for reinforcements. With want of foresight, Rosecrans made a movement of troops from the right just as that portion of the army was about to be attacked by Longstreet. Under this general a superior force of Confederates quickly crushed in the Union right, already in confusion, and drove several of the divisions from the field. The remainder joined the flank of Thomas' corps and stood out the remainder of the battle. Rosecrans, seeing defeat on one flank believed that his army was defeated and retired to the rear to prepare for gathering the fugitives. Thomas, who still remained firm, thought otherwise and made every effort to hold the enemy in check. Bragg's army, and especially Longstreet's corps, made desperate attacks to break and route the thin lines remaining under Thomas. It was a struggle between veterans. Several times the bayonets alone remained to keep off the enemy from the Union front. When evening came the troops of Bragg, balked in their endeavors, could not be made to attack again The Union army was saved, and Thomas was the hero of the hour.

By Rosecrans' order the army now retired into Bhattanooga. Bragg advancing occupied the surrounding heights across the river. These were Missionary Ridge, Orchard Knob, and Lookout Mountain. So close upon the town did he press that communication with nashville was about cut off and semi-starvation troubled the troops in the beleagured town. Better times, however, were close at hand. Grant

Was placed in command in place of Rosecrans. Sherman and Hooker from the west and east were sent with reinforcements, and Bragg was again placed on the defensive.

His lines were on the very high mountainous ridges spoken of above and he thought them impregnable. So, confident of success, he sent Longstreet away to blockade Burnside at Knoxville. Grant, when all his men were at hand, made preparations for a general attack. Hooker was to keep the enemy busy at Lookout Mountain, Thomas was to take Orchard Knob, while Sherman was to capture the northern end of Missionary Ridge. Sherman encountered at first much resistance, but Hooker and Thomas carried the heights in their front. Bragg then withdrew all his men on to Missionary Ridge, still confident that he could not be dislodged. Another day's events undeceived him. As Hooker was delayed by a broken bridge, Thomas' corps charged across the valley and up the steep heights driving the enemy. Sherman also carried the northern position of Bragg, and the Confederate army was in full retreat. Chattanooga was safe, and henceforward the base of supplies. The states of Tennessee and Kentucky were secure, and the way was opened for an attack upon the very centre of the Confederacy which was to cut it in two.