The Eighteenth regiment of Massachusetts Volunteers, under the command of Colonel James Barnes, of Springfield, left their camp at Readville, near Dedham, this afternoon for the seat of war. The regiment numbers eight hundred and seventy men, but will be recruited to one thousand and forty within a few weeks. They are uniformed in the conventional blue and gray of Massachusetts, armed with Springfield muskets of 1842, and fully equipped. They have camp equipage, company wagons and ambulances, and sixty horses, a band of twenty-five pieces enlisted for the war, twenty-five thousand rounds of ball cartridges, and twenty-five thousand rounds of buckshot, and, in fact, all the paraphernalia of  war ready to fit them for immediate service in the field. Of the officers, many are specially qualified for their positions. Col. Barnes is distinguished for having been in the same class with Jeff. Davis, at West Point, graduating A one, when Jeff. was No. twenty-seven, in a class of thirty-one. Lieut.-Col. Ingraham was in the Massachusetts Fourth, stationed at Fortress Monroe. Major Hayes is a graduate of Harvard College, and quite popular. Adjutant Hodge was an officer of the Massachusetts Fifth, and distinguished himself at Bull Run, saving the life of Col. Lawrence. Surgeon Smith was educated in Paris, and was connected with Major Cobb's battery. Other officers of the regiment have seen active service. Most of the men are farmers and mechanics, of moderate means, excellent health, and unwavering devotion to the cause of the Union.--N. Y. Times, August 28.
A correspondent of the Philadelphia Inquirer gives an extended account of a visit of the privateer “Sumter” to Puerto Cabello, together with a copy of a letter from Raphael Semmes, her commander, to the governor of that place.--(Doc. 9.)
A battle occurred at Summersville,1 in Western Virginia, this morning. The Seventh Ohio regiment, Colonel Tyler, was surrounded whilst at breakfast, and attacked on both flanks and in the front simultaneously. The national forces immediately formed for battle and fought bravely, though they saw but little chance of success. The rebels proving too powerful, Col. Tyler sent forward to the baggage train, which was coming up three miles distant, and turned it back toward Gauley Bridge, which place it reached in safety. Companies B, C, and I suffered most severely. They particularly were in the hottest of the fight, and finally fought their way, through fearful odds, making great havoc in the enemy's forces. The rebel force consisted of three thousand infantry, four hundred cavalry, and ten guns. The Union forces scattered, after cutting their way through the enemy, but soon formed again and fired, but received no reply or pursuit from the enemy. Not over two hundred were missing, out of nine hundred engaged. The rebel loss was fearful. Lieut.--Col. Creighton captured the rebels' colors and two prisoners. The following is a list of national officers known to be killed: Captain Dyer, Company D, of Painesville; Captain Shurtleff, Company C, of Oberlin; Captain Sterling, Company I; Adjutant Deforest, of Cleveland; Lieutenant Charles Warrent; Sergeant-Major King, of Warren. The field-officers are all safe.
The Twenty-fifth regiment of Indiana Volunteers left Evansville for St. Louis, Mo.--Louisville Journal, August 28.
Henry Wilson, Senator from Massachusetts, was commissioned to organize a regiment of infantry, with a battery of artillery and a company of sharpshooters attached. In his call he asks the loyal young men of Massachusetts, who fully comprehend the magnitude of the contest for the unity and existence of the Republic, and the preservation of Democratic institutions in America, to inscribe their names upon the rolls of his regiment, and to leave their homes and their loved ones, and follow our flag to the field.
The War Department issued an important order, prohibiting all communication, verbally or by printing or telegraph, respecting the operations of military movements, either by land or sea, or relating to the troops, camps, arsenals, intrenchments, or military affairs, within any of the military districts, by which information shall be given to the enemy, under the penalty prescribed by the Fifty-seventh Article of War, which is death, or such other punishment as a court-martial shall impose.--(Doc. 11.)
The Postmaster-General of the United States, acting under the proclamation of the President interdicting commercial intercourse with the seceded States, directed the postal agents of the Government to put an end to transmission of letters to the seceded States, by the arrest of any express agent or other persons who shall hereafter receive letters to be carried to or from those States.--(Doc. 12.)
Captain Foote was ordered to the command of the United States naval forces on the Western waters — namely, the Mississippi, Missouri, and Ohio rivers.--N. Y. Herald, August 27.
A Naval and military expedition sailed from Fortress Monroe, under the joint command  of Commodore Stringham and Major-General Butler. It consisted of the frigates Minnesota and Wabash, the sloop-of-war Pawnee, gunboats Monticello, Harriet Lane, and Quaker City, with numerous transports.--See Aug. 29.
A camp of instruction at Scarsdale, Westchester County, N. Y., was opened under command of Brigadier-General E. L. Viele. The camp is about seventy acres in extent, situated on an upland which gradually slopes toward the Bronx River, where there is excellent bathing. All regiments and companies recruited, and not imperatively needed at Washington, as fast as they are sworn in, will be sent to this camp, and there subjected to the most thorough drill and discipline. General Viele has adopted stringent and wholesome regulations for the government of his camp. All officers are required to stay in camp, and put up with soldier's fare, instead of dissipating their time in the city. No officer will be allowed to wear the insignia of rank until he is sworn in. All the other rules in use among the regular service, for the government of camps, will be enforced at Scarsdale. The name of the new encampment is “Camp Howe.” --N. Y. Commercial, August 27.
Colonel Jones, of the Fourth Alabama regiment, died at Orange Court House, Va., from wounds received in the battle of Bull Run.