534 THE POPULAR SCIENCE MONTHLY. 



three feet of water. It attained a speed of ten miles an hour, and 

 towed an American packet-ship, the Toronto, four and a half miles 

 an hour on the Thames. This was a splendid success. 



Ericsson built several screw-boats, and finally, meeting Captain 

 Robert F. Stockton, of the United States Navy, that gentleman was 

 so fully convinced of the merits of Ericsson's plans that he ordered 

 an iron vessel of seventy feet length and ten feet beam, with engines 

 of fifty-horse power. 



The trial of the Stockton, in 1839, was eminently satisfactory. 

 The vessel was sent to America under sail, and the designer was soon 

 induced to follow her to this country, where his later achievements 

 are well known. 



The engines of the Stockton were direct-acting, the first examples 

 of engines coupled directly to the crank-shaft without intermediate 

 gearing, that we meet with after that of John Stevens. 



99. Soon after Ericsson arrived in the United States, he obtained 

 an opportunity to design a screw-steamer for the United States Navy, 

 the Princeton, and, at about the same time, the English and French 

 Governments had screw-steamers built from his plans, or from those 

 of his agent in England, the Count de Posen. 



In these ships the Amphion and the Pomone the first horizon- 

 tal, direct-acting engines ever built were used. They were fitted with 

 double-acting air-pumps, having canvas valves and other novel feat- 

 ures. 



From 1840 the screw gained favor rapidly, and finally began to 

 displace the paddle for deep-water navigation. Progress in this di- 

 rection was at first somewhat slow. 



In 1840, and during the following ten years, many experiments 

 were instituted between the performance of screw and paddle steam- 

 ers without definitely settling engineering practice. 



100. The reason was, probably, that the introduction of the rapid- 

 ly-revolving screw, in place of the slow-moving paddle-wheel, neces- 

 sitated a complete revolution in the design of their steam-engines. 

 And the unavoidable change from the heavy, long-stroked, low-speed 

 engines, previously in use, to the light engines, with small cylinders 

 and high piston-speed, called for by the new system of propulsion, 

 w T as one that necessarily occurred slowly, and was accompanied by 

 its share of those engineering blunders and accidents that invariably 

 take place during such periods of transition. 



Engineers had first to learn to design such engines as should be 

 reliable under the then novel conditions of screw-propulsion, and 

 their experience coidd only be gained through the occurrence of 

 many mishaps and costly failures. The best proportions of engines 

 and screws for a given ship were determined only by long experience, 

 although great assistance was derived from the extensive series of 

 experiments made on the French steamer Pelican. It also became 



