I enter here upon no discussion of the character of the late Commander Slidell Mackenzie, but observe simply that no one can read Mr. Cooper's volume upon the battle of Lake Erie and retain a very profound respect for that person's sagacity or sincerity. The proprietors of the copyright of Mr. Cooper's abridged Naval History offered it, without his knowledge, to John C. Spencer, then Secretary of the State of New-York, for the school libraries of which that officer had the selection. Mr. Spencer replied with peculiar brevity that he would have nothing to do with such a partisan performance, but soon after directed the purchase of Commander Mackenzie's Life of Commodore Perry, which was entirely and avowedly partisan, while Mr. Cooper's book was rigidly impartial. Commander Mackenzie returned the favor by hanging the Secretary's son. A circumstance connected with this event illustrates what we have said of obtaining justice from the newspapers. A month before Commander Mackenzie's return to New-York in the Somers, Mr. Cooper sent to me, for publication in a magazine of which I was editor, an examination of certain statements in the Life of Perry; but after it was in type, hearing of the terrible mistake which Mackenzie had made, he chose to suffer a continuation of injustice rather than strike a fallen enemy, and so directed the suppression of his criticism. Nevertheless, as the statements in the Life of Perry very materially affected his own reputation, in the following year, when the natural excitement against Mackenzie had nearly subsided, he gave his answer to the press, and was immediately accused in a "leading journal of the country" of having in its preparation devoted himself, from the date of that person's misfortune, to his injury. The reader supposes, of course, that the slander was contradicted as generally as it had been circulated, and that justice was done to the forbearance and delicacy with which Mr. Cooper had acted in the matter; but to this day, neither the journal in which he was assailed, nor one in a hundred of those which repeated the falsehood, has stated these facts. Here is another instance: The late William L. Stone agreed with Mr. Cooper to submit a certain matter of libel for amicable arbitration, agreeing, in the event of a decision against him, to pay Mr. Cooper two hundred dollars toward the expenses he must incur in attending to it. The affair attracted much attention. Before an ordinary court Mr. Cooper should have received ten thousand dollars; but he accepted the verdict agreed upon, the referees deciding without hesitation that he had been grossly wronged by the publication of which he had complained. After the death of Mr. Stone one of the principal papers of the city stated that his widow was poor, and had appealed to Mr. Cooper's generosity for the remission of a fine, which could be of no importance to a gentleman of his liberal fortune, but had been answered with a rude refusal.