Political parties are losing their sway. Higher than party are country and the duty to save it from Cæsar. The Caucus is at last understood as a political engine moved by wire-pullers, and it becomes more insupportable in proportion as directed to personal ends. Nor is its character changed when called a National Convention. Here, too, are wire-pullers; and when the great Office-Holder and the great Office-Seeker are one and the same, it is easy to see how naturally the engine responds to the central touch. A political convention is an agency and convenience, but never a law, least of all a despotism; and when it seeks to impose a candidate whose name is a synonym of pretensions unrepublican in character and hostile to good government, it will be for earnest Republicans to consider well how clearly party is subordinate to country. Such a nomination can have no just obligation. Therefore with unspeakable interest will the country watch the National Convention at Philadelphia. It may be an assembly (and such is my hope) where ideas and principles are above all personal pretensions, and the unity of the party is symbolized in the candidate; or it may add another to Presidential rings, being an expansion of the military ring at the Executive Mansion, the senatorial ring in this Chamber, and the political ring in the custom-houses of New York and New Orleans. A National Convention which is a Presidential ring cannot represent the Republican Party. Much rather would I see the party to which I am dedicated, under the image of a life-boat not to be sunk by wind or wave. How often have I said this to cheer my comrades! I do not fear the Democratic Party. Nothing from them can harm our life-boat. But I do fear a quarrelsome pilot, unused to the sea, but pretentious in command, who occupies himself in loading aboard his own unserviceable relations and personal patrons, while he drives away the experienced seamen who know the craft and her voyage. Here is a peril which no life-boat can stand. Meanwhile I wait the determination of the National Convention, where are delegates from my own much-honored Commonwealth with whom I rejoice to act. Not without anxiety do I wait, but with the earnest hope that the Convention will bring the Republican Party into ancient harmony, saving it especially from the suicidal folly of an issue on the personal pretensions of one man. INTEREST AND DUTY OF COLORED CITIZENS IN THE PRESIDENTIAL ELECTION. LETTER TO COLORED CITIZENS, JULY 29, 1872. I will say to the North, Give up; and to the South, Keep not back.--ISAIAH, xliii. 6. * * * * * The immediate occasion of the present Letter appears in the following, from colored citizens of Washington to Mr. Sumner:-- WASHINGTON, D. C., July 11, 1872.