In lus recent letter declining a nomination for the Const'tutional CÃ³hvention, Gov. Seward writes : I want no War - I want rio enlargement of territory,sooner than it would come if wo wero contented with a niasterly innctivity. I abhor war, as Idetest Slavery. I would not givo ono human life for all the Continent that remains to be annexed. Uut I cannot exclude the conviction that iho popular passion for Territorial aggrandizement is irresistible. Prudenco, Justice, Cowardice, may check it for a season, but it will gain strength by ils subjcction. An American army is at the heart of what was Mexico. Let the Oregon question bo settled when it may, it will, neverthele&s, come back again. Our population is destined to roll its resistlcss waves to the barriers of the North, and to encounter OrientalCiviJizalion on the shores of the Pacific. The Monarchs of Europe are to have no rest, whilc they have ccolony remaining on lliis Continent. France has already sold out. Spain has sold out. We shall see how leng bcfore England inclinees 10 follow their example. It behoves us, then.to qualify ourselves forour mission. We must dare our destiny. We can do this, and can only do it, by carly measures which shall efTect the abolition of Slavcry, without Precipitancy, without Oppression, without Injustice to Slaveholdors, wiihout Civil YVar, with the consent of mankind and the approbation of fleaven. The restoralion of the Right ofSuirrageto freemen, is tho first act, and will draw after it, in due time, the sublime cafaslropho of Emancipation."