A gentleman direct from Baltimore, and who has seen the steam-gun (about which considerable has been said) operate, has furnished us with the following description of it:  

It is on four wheels; the boiler is like that of an ordinary steam fire engine, the cylinder being upright. There is but one barrel, which is of steel, on a pivot, and otherwise is like an ordinary musket barrel. It is fed or loaded through a hopper entering the barrel directly over the pivot. The barrel has a rotary motion, and performs the circumference, by machinery attached, at the rate of about sixteen hundred times a minute. The balls are let into the barrel through a valve at will, and every time the barrel comes round to a certain point, another valve, self-operated, lets out a ball, which is propelled solely by the velocity of the barrel in revolving.  

Washington, Sunday Evening, May 5.  

Yesterday, Gen. Scott forwarded dispatches to Gen. Butler, at Annapolis, placing the Massachusetts Sixth Regiment and other troops at his command, and giving him three days to take possession of the Relay House, at the junction of the Baltimore and Ohio and Baltimore and Washington railways, nine miles from Baltimore and thirty from Washington. Butler responded that he would hold religious services there today. The Sixth Massachusetts Regiment went up early this morning. This movement is made to co-operate with the Pennsylvania troops now advancing upon Baltimore on the other side.

The Secessionists of Baltimore having torn up the railroad track leading from the Northern Depots to the Southern Depots, the military were obliged to march through the City. On the arrival of two Regiments, one from Massachusetts and the other from Philadelphia, on the 19th instant, an attack was made upon them by a mob, with stones, brick-bats & other missiles. This drew a fire from the soldiers, discharging their pieces into the crowd, killing live or six, and wounding many others – among them several innocent spectators. Three of the Massachusetts men were killed and eight wounded. The Philadelphia Regiment was unarmed, and but few of them had left the cars when the riot commenced – some of them, however, seem to have been roughly handled. The train was ordered back, and the Regiment returning to Philadelphia early on Sunday morning.