Meanwhile Francis Pettit Smith in this country had adapted the screw propeller to steam navigation, and after one or two experimental boats had been successful, the _Archimedes_, fitted with a screw propeller of his design, made her memorable journey from port to port of the British Islands in 1838. The _Novelty_, a slightly larger vessel, of 117 feet in length, was launched the next year, both coming from the yard of Mr. Wimshurst, at Blackwall. About this time Ericsson brought out his screw propeller, and having equipped a small steamer with it, towed the Admiralty barge a considerable distance upon the Thames with the Lords of the Admiralty on board, besides making other experiments, all of which were not without a fair measure of success. The navy officials were not convinced, however, that the application of the power at the stern was of practicable value for warships. So Ericsson went to America, and devoted his remarkable inventive genius to the welfare of his adopted country. Had he remained in England, and had his inventions been taken up by the Government, the history of the ’sixties might have been very different, for it was he who designed the _Monitor_, the small turret ship which prevented the Confederates from obtaining the command of the sea in the American Civil War. In 1841, he accepted an order from the United States Government to furnish the designs for a screw warship, the _Princeton_, this being the first vessel which had the machinery wholly below the water-line and out of reach of an enemy’s shot. This vessel is claimed by Americans to have “dictated the reconstruction of the navies of the world.”[31] Several mechanical novelties and contrivances strange to warships, and for the most part owing the form in which they were introduced into this vessel to the fertile brain of the inventor, made their appearance in the _Princeton_. She had a direct-acting, semi-cylindrical steam engine of great compactness and simplicity, independent centrifugal blowers for ventilating the machinery compartment and assisting the combustion in the furnaces, so as to avoid the exposure during an engagement of the smoke stack which, as a greater measure of safety, was made on the telescopic principle. The 12-inch wrought-iron gun, with which the vessel was armed, was the first of its kind, and was at that time the largest and most powerful weapon afloat. He designed the wrought-iron gun carriages, and provided them with contrivances for dispensing with breeching and taking up the recoil. There were also an optical instrument to enable the commanding officer by mere inspection accurately to ascertain the distance of the object to be aimed at.