The lecture room was well filled by the audience who came to hear Mr. Ed. Channing lecture on the "Fitz-John Porter Case," last evening. The lecturer began by saying that Pope's campaign was a failure, chiefly owing to his own incompetence. It was charged, however, that Fitz-John Porter was to blame, and he was tried by a court-martial, and sentenced to be dismissed. This decision was brought up and considered by a court of inquiry in 1878-79, who recommended that the action of the court martial be reversed. Mr. Channing then explained the maps which he had brought with him, and showed the position of the armies. He explained the famous "joint order" of Pope's to McDowell and Porter, and the way in which Porter misunderstood it, and hence did not move. After some correspondence Gen. Porter attempted to move, but it was too late. The lecturer then took up Pope's charge that Porter wilfully kept his troops out of the contest, although he knew that his force was needed. This was founded entirely on wrong assumptions, viz., that Porter had advanced as far as the Gap, and that a terrific battle took place on Aug. 29th.

This last assumption was based on a report of Gen. Jackson with its date changed by Pope's friends. In fact, as Pope's chief officers testified, the only sound of fighting during the day was that of a few volleys of musketry towards evening. Mr. Channing then showed the falsity of the second allegation, citing the testimony of Longstreet and his officers. It was then pointed out that the testimony of Pope's friends about the "4.30 order" was decidedly suspicious, and that Porter did not receive the order until about 6.30 P. M., as several of his staff and officers testify. Porter's note to McDowell at six o'clock also bears on its face the fact that he had not received the 4.30 order. It was also impossible for Porter to fulfil the order, because the position, both of the enemy and of the Federal troops was different from what the writer of the order supposed. The lecturer then took up another charge against Porter concerning his not moving on the night of the 28th and 29th. He showed that this move was impossible, since the night was pitch dark and the men had already marched nineteen miles that day and the artillery was not able to move. This is the charge which Porter's enemies have taken up during this winter, having been utterly refuted on the other charges. Mr. Channing closed by reading an extract from the report of the Schofield court, which completely exonerates Gen. Porter and shows that his conduct was most exemplary.