Complex sentence: The August 1855 edition (starting about halfway down the PDF Feb.1855 edition), says that Harrier was in the Baltic, and Young was not on it because he had joined the flagship, as secretary to the Captain of the Fleet, Commodore Hon Fred.
Split into simpler sentences: The August 1855 edition (Starts about ½-way down the pdf Feb.1855 edition), says that Harrier was in the Baltic, and Young was not on it. That's because he had joined the flagship, as secretary to the Captain of the Fleet, Commodore Hon Fred.