Washington, May 14.- The navy department has received the followingr dispatch from Sampson. It is dated St. Thomas, May 12, and is as follows: "A portion of the squadron under my command reached San Juan this morning at daybreak. No armed vessels were found in the port. As soon as it was sufficiently light I commenced attack upon the batteries defending the city. This attack lasted about three hours and resulted in much damage to the batteries and incidentally to a portion of the city adjacent to the batteries. The batteries replied to our fire but without material effect. One man was killed on board the New York and seven slightly wounded in the squadron. No serious damage to any ships resulted. SAMPSON." Admiral Sampson's statement that he attacked with only a portion of nis fleet is taken to indícate that he did not find it expedient to take the entire squadron into the harbor, though it is not believed he has separated his fleet. A special from St. Thomas says the casualties on board the United States fleet in the bombardment of San Juan were as follows: Killed- Seaman Frank Widemark of the New York. Wounded - Samuel Feitman, leg broken, and four other seamen on the New York: Marine M. G. Merkle, elbow broken; Seamen R. C. Hill and John Mitchell. slightly hurt.