Arsenal et Harper's Ferry.
The Washington correspondent of the New York Herald says that Hon. A. R. Boteler, representative from the Charlestown District, has received a letter similar to the one received by the War Department on the night of the John Brown raid, in which the writer pretends to expose a plot for another inroad into Virginia, in which a large force is said to be enlisted. It is also said that numerous anonymous letters are being received by people in Charleston, threatening all sorts of mischief. There may be no foundation for these rumors; but, in times like the present, and in view of the recently exposed plot to seize the Arsenal in St. Louis, it would be well to have a force at the Harper's Ferry Armory sufficient to protect the public arms there deposited, from another incursion.