The Harper's Ferry Outbreak.

Yesterday they spread abroad on the wings of the telegraph, that "correspondence with HORACE GREELEY" had been discovered in "Old Brown's" carpet-bag. The foundation for this was merely a business memorandum that he had once subscribed to the New York Tribune!

To-day the Herald parades under the startling head of "Senators Seward, Sumner, Hale, Wilson, Chase and other Black Republicans implicated in Old Brown's Plot"--a series of documents from one Forbes, in which said Forbes acknowledges having been a former accomplice of Brown, and narrates how he went to several leading Republicans, a year or two ago, to ask their help in a scheme for forcibly "stampeding slaves;" but his own account shows that he got no money and no encouragement from them, nor would they even listen to him after he had developed the nature of his project. Greatly chagrined, he was obliged to abandon it, whereat he vents his spleen in sundry forcible expressions. Instead of proving any complicity with "Slave Insurrection" enterprises, on the part of Republicans, Forbes's revelations prove just the reverse.

But how is it about the Democrats who knew of Brown's Plot two months before it ripened? How about the Secretary of War and the Administration, whose duty it was to protect the Government Armory at Harper's Ferry, and yet who gave no warning of the coming outbreak, although they had been fully informed of it by Letter? Did they desire the outbreak to occur, in order to make political capital out of it?

These questions have been put once or twice before, but the Democratic Press and the Administration make no reply!