The following is the entry for William Houston Stewart in William O'Byrnes 1849 'Naval Biographical Dictionary'.
STEWART. (Commander, 1848. f-p., 12; h-p., 0.)William Houston Stewart, born in Sept. 1821, is eldest son of Capt. Houston Stewart, R.N., C.B.
This officer entered the Navy, 29 April, 1835, on board the Tweed 20, Capt. Thos. Maitland, from which vessel, after visiting the coast of Africa and serving during the civil war on the north coast of Spain, where he frequently landed as Aide-de-Camp to his Captain, he removed, in 1837, to the Carysfort 26, Capt. Henry Byam Martin. In that ship he took part, except in the capture of Sidon, in all the operations of 1840 on the coast of Syria; where he commanded a boat, and was mentioned by Capt. Horatio Thos. Austin, of the Cyclops steamer, for his judgment and gallantry at the bombardment of the strong castle of Gebail. In the attack upon Tortosa he again had charge of a boat, and was twice grazed and severely contused by musket-balls. On the paying off the Carysfort he joined, towards the end of 1841 (he had passed his examination 30 April in that year), the Illustrious 72, flag-ship on the North America and West India station of Vice-Admiral Sir Chas. Adam, by whom he was promoted, 29 June, 1842, to a death-vacancy in the Volage 26, Capt. Sir Wm. Dickson. Of her he was for six months senior Lieutenant in the West Indies. In March, 1843, he went back to the Illustrious; and in Feb. 1844, the latter ship having nearly served her time, he was appointed, at his own request and that of his Captain, John Erskine Loch [should be John Elphinstone Erskine], First of the Ringdove 16, Capt. Sir Wm. Daniell. He subsequently proceeded to the coast of Africa; where, on being superseded by an officer appointed by the Admiralty, he volunteered (although offered a passage either to England or to his proper station. North America and the West Indies) to serve as a Supernumerary with Commodore Wm. Jones in the Penelope steam-frigate. This he continued to do until a severe attack of fever induced him to yield to the friendly solicitation of his chief; when he returned home in an Indiaman, carrying with him a letter so laudatory of his zeal and merits that the Admiralty allowed him full pay until the period of his arrival. He was then at once, on the application of Capt. Armar Lowry Corry, appointed, 8 Jan. 1845, to the Superb 80, fitting at Portsmouth. In Nov. of the same year, his former Captain, Martin, having obtained command of the Grampus 50, Mr. Stewart was permitted, at his request, to join him; and in the early part of the ensuing year he sailed for the Pacific. He came home at the commencement of 1847; was nominated, 29 Dec. in the same year, Flag-Lieutenant, in the Ocean 80, to Sir Edw. Durnford King, Commander-in-Chief at Sheerness; and on 19 May, 1848, was advanced to his present rank.
When the Superb was fitting out at Plymouth, Commander Stewart jumped overboard, an ebb-tide running at the time, and, nearly at the cost of his own life, saved that of a marine. For this humane and intrepid act he received the thanks of the Royal Humane Society on vellum.