If space permitted, it would be interesting to trace the career of Ericsson in detail after the success of the Monitor. There was an imperative demand for armor-clads, and ere long several were built by the inventor and his associates. Ericsson was never idle. In connection with his labors upon war vessels he expended no small amount of ingenuity on the improvement of heavy guns, his efforts in this field being directed by a most exhaustive study into the strength of materials, the operation of explosive forces, and the laws governing the flight of projectiles. In 1869 he constructed for the Spanish Government a fleet of thirty steam gunboats, intended to guard Cuba against filibustering parties. In 1881 he devised his latest war vessel, the Destroyer, the object of which he said was "simply to demonstrate the practicability of submarine artillery, unquestionably the most effective, as well as the cheapest, device for protecting the sea-ports of the Union against iron-clad ships. I do not," he continued, "seek emoluments, as I am financially independent; but I am anxious to benefit the great and liberal country which has enabled me to carry out important works which I should not have carried out on a monarchical soil." His investigations included computations of the influences which retard the earth's rotary motion; he erected a "sun motor" in 1883, to develop the power obtained from the supply of mechanical energy in the sun, and he contributed numerous valuable papers to various journals in America and Europe on scientific, naval, and mechanical themes. The year in which John Ericsson reached the culmination of his fame, 1862, was the same in which his brother Nils retired from active life in Sweden. The latter had retained his position on the Göta Canal when his brother left it in 1820, and gradually won his way to fame and fortune. "He was a man of industry and energy, of sterling integrity and public spirit, and an excellent organizer; while his conservative and cautious temperament and his skill in bending others to his purposes enabled him to make the most of his opportunities." After he received his title he altered the spelling of his name and became Baron Ericson. This change gave great offence to John, who wrote to Nils: "I can never forget the unpleasantness caused me by this annulling of relationship. Possibly your wife has had her share in it. If so, she will find some day that the blotted-out letter will cost her children half a million."