John Merryman, esq., of Baltimore county, President of the Maryland Agricultural Society, was arrested on Friday of last week, by order of the Government, and taken to Fort McHenry to await an investigation on a charge of Treason. On the petition of the prisoner, Roger B. Taney, Chief Justice of the Supreme Court, on Sunday issued a writ of habeas corpus, which was served on Gen. George Cadwallader directing him to produce the body of Merryman in Court by 11 o’clock, Monday.  

At the appointed hour Colonel Lee appeared in Court and slated that lie was instructed by General Cadwallader to express his regret that pressing duties in connection with his command prevented his appearing before his Honor in person, and to present his response to the writ. General Cadwallader in his reply states that Merryman was not arrested with his knowledge or by his order or direction, but by Col. Yohe acting under order of Major Keim,“ and is charged with various acts of treason, and with being publicly associated with and holding a commission as Lieutenant in a company having in their possession arms belonging to the United Slates, and avowing his purpose of aimed hostility against the Government.

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.