Sanders Theatre was crowded last evening by an audience which, even more than at the previous lectures, showed its quick interest and depth of feeling by loud applause at the appearance of each well known face upon the sheet. Grant, Sheridan, Sherman, Hooker and, above all, Thomas were enthusiastically received.

The substance of the lecture was as follows:

Next to Richmond, in the East, and Vicksburg, in the West, Chattanooga, the stronghold which guarded the Confederate centre, was the most important strategic point, toward which the Union armies were struggling. With its strong natural defences, and its importance as a railroad centre, Chattanooga not only protected the heart of the South from Federal invasion, but it also opened up for the rebels an easy path into Tennessee and Kentucky.

For six months after the battle of Stone River the two armies lay facing each other at a distance of thirty miles. Hard fighting had been tried without much effect, and each now tried, by cavalry raids, to cut the other's line of communications.

Rosecrans at length advanced, driven on by Northern impatience. Here there was no navigable river to make the advance easy, but, by skilful manoeuvering, Bragg was forced back into Chattanooga without a battle. By July 3, 1863, Rosecrans had determined to drive the Confederates still further back.

The problem was difficult. The crooked Tennessee River had to be passed, as well as rough mountainous country. The most direct road was to move around the town, north of the river, and attack from the northeast. But this road was long and far from the base of supplies. Moreover, Bragg expected the attack in that quarter.

For these reasons, Rosecrans adopted the bold plan of striking directly south, across the river and over a succession of mountain ridges, passable only by narrow gorges, to the railroads which brought Bragg his supplies from the South.

To conceal the movement Crittenden was sent far round, by the first road to attract Bragg's attention. And just here was the fatal mistake. The Union line was drawn out for 50 miles, over rough, hostile country. McCook, on the right, was several days' march distant from Thomas, in the centre. Now Bragg suddenly evacuated Chattanooga and appeared, with his whole force of 50,000, opposite Thomas. If he had attacked then, he would have won a complete victory.

But Bragg waited for Long street's arrival from Virginia with reinforcements. He then attacked, striking with wonderful good fortune a gap, left by a misunderstanding, in the Union centre. Six whole divisions burst through and hurled back the Federal right in utter confusion. Rosecrans himself was drawn into the flight and thought all was lost. At this crisis, Thomas threw himself in the breach, and by his heroic firmness and skill, held the road to Chattanooga for six hours, against the whole strength of the victorious enemy. His force of 25,000 dwindled to 15,000. Ammunition gave out. But the gallant division repelled the last charge with cold steel, and withdrew at nightfall in perfect order. A grander resistance can not be found in the annals of history.

After this murderous conflict in which, out of a total of 125,000 men, 37,000 were lost, Rosecrans found himself cooped up in Chattanooga, almost without supplies. The Confederates, on the heights above, stretching from one point on the river around the town to the river again, awaited with confidence the time when starvation would compel the Union army to surrender.

The outlook for Rosecrans was gloomy. New leaders, however, were soon to take charge. Oct. 19 Grant was made commander of all forces west of the Alleghanies, and his first step was to put Thomas in Rosecrans's place. Grant himself hastened to the spot, and Hooker arrived from Virginia with 23,000 men.

The first thing was to open a line of communication to the besieged force. This was most adroitly accomplished by Gen. W. F. Smith, who planned a new road, crossing the river twice, and passing just out of reach of the Confederate guns on Lookout Mountain to Bridgewater, the terminus of the Northern railroad. A footing was secretly gained on the hills commanding this line, much to Bragg's chagrin, and supplies soon poured in.

Grant was now eager to take the initiative. But Bragg was blind to the change in affairs and detached a strong force to attack Burnside in Knoxville.

The Union plans were soon formed. Sherman, lately arrived from Mississippi, was to attack the Confederate left, and threaten their base of supplies at Chickamauga Station. This point was very strong, but the attack was to be unexpected, and Thomas in the centre, and Hooker on the left were to attack at once, if the troops opposite them were drawn away to oppose Sherman.

This plan, simple and effective, was carried out to the letter. With unrivalled skill, Sherman made a long detour, and, wholly unexpected, gained a strong foothold on Bragg's right. Thom as also advanced and took a firm stand on the foot-hills. It was then, profiting by Bragg's confusion, that Hooker made his brilliant capture of Lookout Mountain. His troops had to move painfully around the edge of the mountain from west to east, before they could so much as find a place for ascent. At last they reached a winding cart-track, and up they went, until the clouds hid the death-struggle from the watchers. In a few minutes more it was all over, and the enemy was in full retreat down the slope.

Next morning Thomas in turn attacked. Again the Union charge was invincible. Though ordered to pause at the first line, the troops swept on to the very top of Missionary Ridge, in a resistless wave. Hooker took the enemy in the flank, and on the distant left, Sherman completed the victory.

A peculiar interest attaches to the campaign through its wildly picturesque and beautiful surroundings, but in the military ability displayed by the great leaders, and in the reckless courage of the troops, Chattanooga has become a monument to the defenders of the Union. Its strategie results cannot be overestimated. Grant, having crushed one flank and the centre of the Confederacy, was now called to crush the one vigorous point of resistance, Lee in Virignia.