The State A'etvs, " by request of a large numler of Republicana, and sorae Democrats," has reproduced the " Casa-Nicholson Letter." 'The N.ivs has dono a good thii)g, and in the language of the play, we may well exclaira, " We thank thee, Jew." We hope that the Republicans will read this letter, and read it carefully. In it they will find proof positive that the Democratie party occupies no new ground concerning the power of Congress over the subject of slavery in the Territories. This letter of Gen. Cass was written in 1847, and it plainly, pointedly, unmistakably denied the power of Congress, under the Cooatitution, to legislate upon the subject of slavery in thé Territories, and as plainly and positively claimed for the people of the Territories the riglit to settle the question for themselves. Tbis was the doctrino of Gen. Cass in 1847, established by the Nicholson letter, established by his speeches and votes in the Senate, established by bis refusal to obey instructions to vote for the Wilraot Proviso, and accepted and adopted by the Democratie party. Thii letter was written in 1847 ; ia May, 1848. Gen. Cass was nomsnated for tho Presidency by the Democratie party, in National Convention assembled at Baltiinore, and placed upon a platform embodying the Popular Sovereignty doctriue of his Nicbolsou letter. His opinions were known, and approved by the highest power known to the party. The personal dtfection of Martin Van Bu rex, and tho dissatisfaction of tho extremists at the South with the position of Gen. Cass and the platform upon the slarery questiou alone, causod his djféat and the election of Gen. Taylor. Uut in 1852 Gen. Pierce was nominated, and the same plank put in the platform. The Whig leaders in sustaining the Compromiso raeasures of 1850 had come upon the same ground, and in that campaign the issue was not distinctly defined. In 185G Buchanan was nominated upon a Popular Sovereignty platform, and Fremont was placed upon a platform bustaining the power of Congress. The issue thus directly made up, is the issue uow. Douglas and the Dumocratic party adliere to the doctrine of the " CassNicholsou letter," and aflirm tho right of the Territories to regúlate their own domestic aflfair in their own way, while Lincoln and the llepublicans huid to the old British doctrine - the doctrine that lost Gcorge the III. thirteen jewel3 from his crown - that the Territories are colonies, and that Congress has the exclusive right to legisiate for them. The Nicholson letter discusses the issue fairly ; it was sound Democratie doctrine in 1847 ; it is sound Democratie doctrine to-day ; and agaiu we thank the Newt for re-producing it. We hope that it will insert it weekly'until after the election. JC3E" The Republican journals abound in glurs upon the mother and wife of Douolas. The Democratie papers treat with respect or say nothing about the wife and daughters of Lincolk. ty The llepublican journals are annonncing the conversioii of Tom Kwnu. W'ordcrfal !