MACKENZIE, Alexander Slidell, naval officer, born in New York city, 6 April, 1803; died in Tarrytown, New York, 13 September, 1848. He was the son of John Slidell, and the brother of the United States senator of that name. The name of Mackenzie, that of his mother, was added to his own in 1837, at the request of a maternal uncle. He entered the navy as midshipman in 1815, and in 1822 he took command of a merchant-vessel to improve himself in seamanship. He was made lieutenant in 1825, and commander in 1841, and in both grades was in active duty in the Mediterranean, the West Indies, the Brazilian waters, mid the Pacific. He was at Bahia in command of the "Dolphin " during the siege of that place, and at its surrender, and was an eyewitness of many of the political events on the Rio de la Plata at that period, an account of some of which he published in a pamphlet at the time. He also enjoyed the intimacy of General Rosas, with whom he subsequently corresponded for many years. In 1842 he had charge of the brig "Somers," manned chiefly by naval apprentices; and on his passage from the coast of Africa, in the autumn of that year, the existence of a mutinous plot on board was discovered, the principals of which were immediately placed in close confinement. A council of officers was called, which, after a careful investigation, recommended the immediate execution of the three persons that were principally implicated. This recommendation was carried into effect at sea, 1 December, 1842. The " Seiners" soon afterward arrived in New York, when a court of inquiry was immediately ordered to investigate the affair. The result was a full approval of the conduct of Mackenzie. Subsequently a court-martial was held upon him at his own request, and the trial again resulted in his acquittal. As the young men that had been executed were all of good social standing, one of them being a son of the secretary of war, John C. Spencer, of New York, the event created a great sensation, and Mackenzie's conduct was as severely criticised by some as it was warmly defended by others. The decisions of the courts-martial did not succeed in quieting these differences of opinion, and the affair more or less embittered the remainder of Mackenzie's life. In May, 1846, he was sent by President Polk on a private mission to Cuba, and thence sailed to Mexico. He was ordnance-officer at the siege of Vera Cruz, and commanded a detached division of artillery at the storming of Tabasco in 1847. Mackenzie also attained note as an author. His first book was "A Year in Spain, by a Young American" (2 vols., Boston, 1829; London, 1831; enlarged ed., 3 vols., New York, 1836), which gained immediate popularity both in this country and in England. "** Ilere," wrote Washington Irving from London on its appearance, "it is quite the fashionable book of the day, and spoken of in the highest terms in the highest circles." it has also been translated into Swedish. His other works are " Popular Essays on Naval Subjects " (2 vols., 1833); "The American in England" (2 vols., 1835) ; "Spain Revisited" (2 vols., 1836) ; "Life of John Paul Jones" (2 vols., Boston, 1841); "Life of Commodore Oliver H. Perry" (2 vols., New York, 1841) ; and" Life of Commodore Stephen Decatur," being vol. xxi. in Jared Sparks's "Library of American Biography" (Boston, 1846). He also left in manuscript "A Journal of a Tour in Ireland." See "The Case of the 'Seiners'; Defence of A. S. Mackenzie" (New York, 1843).--His son, Ranald Slidell, soldier, born in Westchester county, New York, 27 July, 1840, was graduated at the United States military academy in 1862. and assigned to the engineers. In August he was brevetted 1st lieutenant for "gallant and meritorious services" at the battle of Manassas, where he was wounded. He was commissioned 1st lieutenant, 3 March, 1863, brevet captain for gallantry at Chancellorsville, and brevet major for the same cause at the battle of Gettysburg. He was promoted captain, 6 November, 1863, brevetted lieutenant-colonel for his services before Petersburg, Virginia, 18 June, 1864, and became colonel of the 2d Connecticut heavy artillery, 10 June, 1864, being brevetted colonel in the regular army in the following October for gallantry at Cedar Creek, and brigadier-general of volunteers for meritorious services at the battles of Opequan, Fisher's Hill, and Middletown, Virginia He was brevetted brigadier-general in the regular army for bravery and also major-general of volunteers in March, 1865. Besides taking part in other engagements, General Mackenzie was engaged in building bridges, constructing rifle-trenches, repairing roads, erecting forts, and other engineering work throughout the war. He was promoted colonel, 6 March, 1867, and brigadier-general, 26 October, 1882. On 24 March, 1884, he was placed on the retired list, having been disabled "in the line of duty."--Another son, Alexander Slidell, naval officer, born in New York city, 24 January, 1842; died in the island of Formosa, China, 13 June, 1867, was appointed acting midshipman. 29 September, 1855, and promoted midshipman, 9 June, 1859, lieutenant, 31 August, 1861, and lieutenant-commander, 29 July, 1865. He served in the "Kineo" at the passage of Fort Jackson and Fort St. Philip in 1862, and in the "Ironsides" at the first attack upon Fort Sumter in 1863. He commanded the boats of the squadron off Charleston in the joint army and navy expedition of 10 July of the same year, which resulted in the capture of the greater part of Morris island. Lieutenant-Commander Mackenzie lost his life while leading a charge against the savages in the island of Formosa. A tablet to his memory has been placed in the chapel of the naval academy at Annapolis, and his fellow-officers cordially approved the opinion of Rear-Admiral Bell, that " the navy could boast no braver spirit, no man of higher promise," than young Mackenzie.