The great discoverer Harvey, on announcing the circulation of the blood, was astonished to find that no person _upward of forty_ received this important truth. The young only embraced it. More fortunate than this discovery, our cause rallies in its support alike the experience of age and the ardor of youth; but it is in the glowing embrace of the young that it finds assurance of victory. Were I able to make myself heard throughout the land, I would say to the young men everywhere who truly love Liberty: “Your candidate has been the renowned pioneer of civilization in unsettled wastes: associate yourselves with him now as pioneers of Liberty in the National Government; help him unfurl at Washington the flag which he first unfurled on the peaks of the Rocky Mountains; and be copartners with him in the glory of redeeming our beloved country.” Present to the young men of Massachusetts, whom you represent, the assurance of my sincere interest in their happiness and welfare, and believe me, my dear Sir, with much regard, Faithfully yours, CHARLES SUMNER. GEORGE H. HOYT, Esq., of the Committee, &c. APPEAL TO THE REPUBLICANS OF RHODE ISLAND. LETTER TO A COMMITTEE, SEPTEMBER 4, 1856. CRESSON, ALLEGHANY MOUNTAINS, PA., September 4, 1856. DEAR SIR,--Were I well, I should regard your letter as a summons. But I am still in the hands of physicians, by whom I am carefully warned against all public effort. Most reluctantly, at this period of our country’s trial, do I submit. Accept for the Convention which will assemble at Providence my best wishes. Let it apply itself with earnestness, diligence, and singleness of purpose to the rescue of our fair land from the tyranny which now degrades it. Here is room for all,--the aged and the young, the Conservative and the Reformer. Surely, Rhode Island, if not utterly disloyal to herself, if not utterly disloyal to New England civilization, if not utterly disloyal to the Republic of which she constitutes a part, will rise up as one man and insist that Kansas shall be secured to Liberty, and that the Slave Oligarchy shall be driven from its usurped foothold in the National Government. At all events, this State, first planted by the Author of Religious Freedom, will see that Human Rights do not suffer through the votes of her children. Believe me, my dear Sir, faithfully yours, CHARLES SUMNER. CONTRIBUTION FOR KANSAS. LETTER TO MESSRS. GREELEY AND MCELRATH, OF THE NEW YORK TRIBUNE, SEPTEMBER 23, 1856. MESSRS. GREELEY AND MCELRATH:--