We regret to say that a most unhappy occurence took place in Watertown on Monday last. While Mr. John Waterman, an aged gentleman, was stooping down near his fire, his son, Sherman Waterman 2d, who had been some time previous confined for lunacy, but was then at large, came behind him, and by a single blow with a piece of board, taken from the fire, laid him dead upon the floor. The blows were repeated three or four times afterwards. The young man is now in confinement, at this town. His mind, we are told, is completely unstrung.