The wisdom and necessity of some such measure as Mr. SEWARD proposed in his last speech in the United States Senate, and Mr. LINCOLN endorsed in his Inaugural—the assemblage of a National Convention—is daily becoming more and more apparent. Our country is in an anomalous condition for which no precedent can be found in its past history, and none in the history of other nations, whose institutions and modes of government are decidedly different from our own. It is not at all strange that a constitutional chart, devised seventy years ago, as the binding, fundamental law of a great Confederacy like this, should be found, in some respects, defective, or not sufficiently explicit upon subjects of vital importance and of universal interest. There is scarcely a State Constitution in the Union which has not undergone numerous, and in some cases radical and thorough changes. There is scarcely a Government in the world, except our own, where any degree of enlightenment and civilization prevails, which has not been remodelled and changed during the last seventy years in regard to such subjects as are provided for in the Constitution of the United States, and therefore unchangeable by the ordinary processes of American legislation. One important amendment has already received the sanction of twothirds of the members of both branches of Congress, and preparations are being made to submit it to the action of the Legislatures of the different States, so that, when ratified by three-fourths of them, it may become a part of the fundamental law of the land. The Peace Conference, which assembled at Washington last winter, only embodied the wishes of a large portion of the American people, when it prepared and submitted for the consideration of Congress a number of propositions, which are by the citizens of the Border Slave States considered essential to their protection, and which a majority of the people of a number of the free States would, no doubt, cheerfully endorse, if they were submitted to a popular vote for ratification or rejection. The people of the Cotton States have flatly refused to comply with the plain injunctions of the present Constitution, and, after seceding separately from the Union, they have formed a new Confederacy, which has adopted our present Constitution, after incorporating into it a number of important amendments.

Thus, directly or indirectly, quite a general expression of a desire for a modification of our Government has been made. Yet the plans suggested for its change have been so numerous, the propositions presented so diverse in their character, and the difference of opinion in regard to them is so great, that it is probable the nation will never be entirely restored to its wonted state of peaceful tranquillity and harmonious political action until its fundamental law has been thoroughly revised, and a new basis of common agreement arranged. The experiment is not altogether free from danger, it is true, and the assemblage of a National Convention would doubtless bring into contact many antagonistic and explosive theories and opinions; but, after all, this is an inevitable incident of all republican governments, which cannot be effectually administered unless they rest upon the broad basis of a cheerful and willing obedience of the masses of the whole people over whom they assume to rule.

At this particular juncture, there appear to be two especially important reasons for convening such a body, or in some other way changing the Constitution. The prevailing sentiment of the Border Slave States, as far as we are enabled to understand it, undoubtedly is that their safety requires new constitutional guarantees, while the revolutionary condition of the Cotton States is so completely apparent that few can doubt that, if they are to be restored to the Union, its Government must, in some respects, be changed, and if their assumed state of complete independence is to be acknowledged, it should only be clone by the same high and solemn authority that formed the nation they propose to dissolve. The executive, with the consent of the Senate, may, it is true, negotiate treaties; but only with foreign nations and Indian tribes, and not with associate commonwealths. Congress has specific power to admit new States into the Union, but not to authorize or formally permit their departure from it, so that even if it should become apparent that the revolting States were determined to persist in their rash experiment, and all the faithful Union States were perfectly willing to allow them to depart in peace, and to recognize their new Confederacy, the Government, as at present constructed, would have no constitutional right to give full validity to such a movement.

Essential changes of some kind, therefore, appear to be important in any probable event; and until the waves of public opinion, which have been stirred to their profoundest depths by the course of affairs during the last six months, quietly subside into some well-defined and unmistakable channel, constant difficulties, doubts, and uncertainties will probably continue to cast a cloud over the whole destiny of our nation.