On Tuesday April 18, Judge Advocate Burnet made his closing argument for the Government. It was truly a master-piece, complete in every part. It was such an effort as might have been expected, of one who has, during this long tedious trial, shown himself a gentleman, a profound counsellor, a true patriot and an advocate of justice, whose only aim has been to elicit truth, and be the better enabled to serve the true interests of the country. We would gladly present every argument and address he has made, during the trial, but space will not admit, and we therefore invite careful attention to the following sketch of his address: The Judge Advocate, in referring to the accused, said: There are two sides to this case; two sides for the manifestation of sympathy. While here is an old, white-haired man before you, whose every thing is at stake; while here is a father, a generous, open-hearted, and impulsive man, whose all is at stake; and here is a soldier, who has fought in every clime, and who has taken up his sword to destroy life in every cause, whose everything is also at stake, yet there is, on the other side, your Government at stake. If these men be guilty, justice to the nation demands of you this day that you should convict them, and you must not waver. In the consideration of this case, you must bring to your aid a power, that may be a little more than is ordinarily given to human nature. You must, for the time, sink all hatred, malice, even human sympathy; and rise, God-like, to determine the truth and adjust the punishment. That these accused would enter upon the commission of so heinous a crime, I can scarcely permit myself to believe. They have made a strong appeal to your sympathies. Each counsel has advocated the cause of his client with an earnestness and an eloquence that does him honor; I shall always respect them, and bear them in kindly recollection. But there seems to have been something, during these four years of the nation's trial, that has appeared to paralyze the native instincts of the American heart. This phantom, this siren of secession, with her enticing song, seems to have lulled to sleep the better part of human nature. At the sound of her voice, and the flash of her eye, men have sprung to arms, to grapple with the life of the nation, because it was free! They have followed, at the beck of the siren, over desolated homes; they have trampled over the dead corpses of murdered brothers, and innocent women and children. They have blackened the land with desolation, and made it the abode of moaning and woe. She has blinded, while she has demoralized them. Old men, forgetting their white hairs, have joined in the conspiracy at the beck of this phantom, who has taken out of the human heart its heaven-born instincts, to plant there those of vengeance, and the thirst for blood.