Mark Twain gave his new lecture "Roughing It" at Library Hall last night. The audience upon the occasion, evinced in a melancholy degree the truth of the oft quoted assertion that the "public are fickle," for when the genial humorist and man who, by his own confession, says he can tell a lie, but wont, appeared in our city the last time there were many who registered secret and open vows that they never would hear him again being so influenced, partly from the fact that his lecture then was not altogether so brilliant as was anticipated, and partly perhaps because of the exhaustion produced from the merriment occasioned by the few "humorous remarks" he then did make. The vows were doubtless meant to be kept, and may be they were; but somehow there seemed to be no dimunition of the familiar faces at Library Hall last night, and the company being further increased by a large concourse who do not generally find attraction in the lecture hall, the consequence was that Mark was greeted with an immeasurably larger audience than he had heretofore looked upon in Pittsburgh, and one which in every respect has never perhaps been excelled. Some of the people dropped in on Wednesday evening, it is said to "be in time to get a seat." We don't endorse that, but certainly a great many dropped in quite early last evening, and they kept coming until there was no room in the parquette, nor in the parquette circle, nor in the balcony, nor in the gallery away back, and then the aisles were filled with ladies and gentlemen standing and the boxes, even the highest tier could hold no more, and the stage last of all provided accommodation for over a hundred. There would still have been many more in attendance, but they couldn't get in nor within earshot of the speaker, and they formed a mournful procession on the retreat.

The lecturer was somewhat late in coming and in response to the occasional expressions of impatience from the audience, Mr. W. N. Howard about eight o'clock announced that he had arrived in the city but half an hour previous, and was then winding his devious way through Pittsburgh's thoroughfares to the hall. Twenty minutes later a small man, with half-shut dreamy eyes, and a queer, comical expression of countenance, as if its possessor was in doubt whether to laugh or cry, the mouth on the upper side trimmed in with a short, thick, sandy-colored moustache and the chin barren of any hirsute adornment -- a little man arrayed in a black dress suit and supporting a glittering diamond ring on one finger, quietly edged his way through the crowd on the stage, and so quickly that he stood in the centre of the small space reserved for the lecturer before the audience knew what the movement meant. He introduced himself as Mark Twain, adopting as he said that method of getting in all the facts before proceeding with the details of his discourse.

Then audience then for an hour and a quarter were treated to a literary compound of brilliant description and hard material facts, giving the romance and reality of "roughing it" in Nevada, and all picturesquely interwoven with jokes and happy strokes of wit, which came so frequent and were to transparent that the merriment seemed hardly for an instant to cease. And then the most consummate stroke of all was that of which five reporters were made the victims -- five indefatigable pencil destroyers, who for all that hour and a quarter, repressing every outflow of humor, had sedately toiled at their craft and retired elate with the prospect of the rich feast in store for their readers to-day -- prospects which were, alas, dispelled by a call from the genial joker himself, who suavely preferred his request for a suppression of the "notes" taken, for the good of the community and the happiness of himself, as he "traveled some on those remarks." A brother journalist could not be denied, and thus the vision melted away.

Mr. Clemens seemed to be in his happiest vein last night, and never in manner or matter compressed more that was enjoyable. His "roughing it" in the lecture field has evidently given him a new insight into popular feeling, of which he has not been slow to avail himself. The effort financially to the managers, happily to the lecturer, and enjoyably in the highest degree to the people, was a signal success, which has doubly increased the hold of the humorist on popular favor in this community.

The next lecture of the course will be delivered on Tuesday evening next by Olive Logan, who will talk of "Nice Young Men."

Library Hall was crowded to repletion last evening, to listen to Mark Twain's lecture, "Roughing It." The gentleman did not arrive in the city until a short time before the hour announced for his appearance, and the consequence was that the large audience was kept in waiting for some time before Mr. Twain made his appearance. He was preceded by Mr. Howard, of the Lecture Committee, who announced that the next lecture of the course would be delivered on Tuesday evening by Olive Logan, when she will discourse on "Nice Young Men."

On making his appearance Mr. Twain introduced himself in a very humorous manner. He then gave some very interesting descriptions of life in Nevada, its mountains, lakes and rivers; the inhabitants, soil, birds, beasts, &c., which were most pleasantly interwoven with a series of telling jokes, humorous hits, and apparently unconsciously delivered sallies of wit which convulsed the entire audience in the most uproarious laughter. To publish one of the lecturer's humorous points would be but to debar a host of the readers of the COMMERCIAL in other cities in this vicinity, where Mr. Clemens will appear, from enjoying them as they fall from the lecturer's lips.

All present last evening appeared to thoroughly enjoy "Roughing It," and manifested their delight in the most effective manner. Mr. Clemens lectures in Kittanning to-night.