In the selection of his materials, Mr. Greeley has made great use of the speeches, messages, letters, and other public documents relating to the different branches of his subject, the essential points of which he often interweaves into his narrative, though in all suitable cases he does not scruple to present from them full and copious citations. In most instances which involve the opinions of his political antagonists, he has confined himself to the latter method. Impressed with the difficulty of exhibiting the views of an opponent with fairness and accuracy, he has wisely preferred to employ the very language of his original authorities, wherever the exercise of perfect impartiality might appear too sublime a virtue for our fallen and frail human nature. In the mutations of opinion, moreover, many persons are apt to forget that the faith, which they zealously defended but two years ago is at war with their present creed. The surest guaranty of exact and satisfactory statements, accordingly, is to fall back on the primitive authentic platform. The subject of compromises, under the Federal Constitution, between the conflicting interests of the country, occupies, of course, a prominent place in these pages, and is treated by Mr. Greeley, as we think, with signal discretion and ability. His views on this point are marked by candor and moderation, though he is firm and uncompromising in his hostility to concession for the purpose of conciliating the Slave-Power. Political compromises, he maintains, though liable to abuse, are the necessary incidents of all governments, excepting pure and simple despotisms. Liberty cannot exist without diversity of opinions. Unless one will is permitted the supremacy over all others, a medium must be sought between widely differing convictions. If a legislature composed of two distinct bodies differs with regard to a special appropriation, a partial concession on each side is often the only practicable mode of adjustment. When the object is unprecedented, or not essential to the general efficiency of the public service, such as the construction of a new railroad, canal, or other public work, the opposition of either house should suffice for its defeat, or, at least, for its postponement. Neither branch has a right to demand from the other conformity with its views on a disputed point as the price of its own concurrence in measures essential to the existence of the government. Hence the movement of the United States Senate in 1849, dictating to the House a certain organization of the Territories, under penalty of defeating the Civil Appropriation Bill, was totally unjustifiable. But the fact should never be lost sight of, that differences of opinion often occur on momentous questions where the rights of each party are equal, and where an ultimate concurrence in one common line of action is essential. Without some mutual concession to adverse views, the union of the States would have been impossible.