Troops arriving at Washington.
Gov. Hicks Proposes neutral ground.
steamer fired upon.
Terrorism at Washington.
preparations for attack.
the Seventh will not invade the South.
the Hessians Dissatisfied.
Alexandria, April 28.
--Four United States vessels--two war steamers and two transports — with Northern troops, passed up the Potomac this morning.
Gov. Hicks, of Maryland, has issued a proclamation recommending that the State occupy a neutral position.
The steamer Adelaide, of the Norfolk line, was fired at by the Harriet Lane, last Friday night, off Rappahannock river, in Chesapeake Bay, and boarded, but allowed to proceed.
Citizens are still compelled to leave Washington, for sympathy with the South.
A large quantity of shell has been landed at Fort Washington, by the Federal Government.
Two men, one from South Carolina and one from Washington, have been confined as prisoners in the Capitol, for being secessionists.
The New York Seventh Regiment declare they will not invade the South, and are in consequence looked upon with suspicion by the Administration.
The Seventy-first New York Regiment, quartered at Inauguration Hall, revolted on account of bad quarters, and had to be removed to the Navy-Yard. 