One introduced about 1855, for North Sea work, was an iron screw steamer with a long parallel middle body which made a capacious ship, the fore and after parts being designed in accordance with his wave-line theory. Another of his cargo vessels, having a greater length of parallel middle body and wave-line ends, had the screw propeller abaft the rudder, which was entirely below the propeller shaft, there being a loop in the rudder stock through which the propeller shaft passed. A second vessel of this type, but rather longer in proportion to its beam, was designed for the Baltic trade, and had the peculiarity that its forecastle extended as far as the midship deck-house. [Illustration: THE “CITY OF GLASGOW” (INMAN LINE, 1850).] The period from 1845 to 1880 is remarkable for the progress made in steam-ship building prior to the general adoption of steel for the construction of ocean vessels. The early history of the Cunard Line has already been related. Before the last wooden Cunarders were built, the Inman Line appeared on the scene with a service of iron steamers with screw propellers, the first being the _City of Glasgow_, launched in 1850 by Tod and McGregor on the Clyde, for a transatlantic service they themselves intended to establish with Glasgow as its headquarters. The side-lever engine of the ordinary type was modified for this vessel, as it was fitted with two beams working across the ship. The cylinders were on one side of the ship, and on the other was a large wheel which geared three to one with ordinary teeth into the propeller-shaft pinion. Her machinery was placed low down in the hold so as to leave her decks as free of encumbrances as possible. She was a three-decked vessel of 1069 tons gross, 227 feet long by 33 feet beam and 25 feet depth; and her engines of 350 horse-power drove a two-bladed screw of 13 feet in diameter and 18 feet pitch. She was designed to carry 52 passengers in the first class; 85 in the second class, and 400 in the steerage, and a crew of about 70. The hull was divided by five water-tight bulkheads into six compartments, and as a further provision for the safety of her passengers and crew she carried six lifeboats. Her fresh-water tanks contained no less than 13,000 gallons. She was barque-rigged, of almost yacht-like lines, and had a graceful clipper bow. The _City of Glasgow_ made a few voyages between Glasgow and New York in the spring and summer of 1850.