Bell constructed several other boats in 1815, and with his success steam-navigation in Great Britain was fairly inaugurated. In 1814 there were five steamers, all Scotch, regularly working in British waters; in 1820 there were 34, one-half of which were in England, 14 in Scotland, and the remainder in Ireland. Twenty years later, at the close of the period to which this chapter is especially devoted, there were about 1,325 steam-vessels in that kingdom, of which 1,000 were English and 250 Scotch. But we must return to America, to witness the first and most complete success, commercially, in the introduction of the steamboat. The Messrs. Stevens, Livingston, Fulton, and Roosevelt were there the most successful pioneers. The latter is said to have built the "Polacca," a small steamboat launched on the Passaic River in 1798. The vessel was 60 feet long, and had an engine of 20 inches diameter of cylinder and 2 feet stroke, which drove the boat 8 miles an hour, carrying a party of invited guests, which included the Spanish Minister. Livingston and John Stevens had induced Roosevelt to try their plans still earlier,[74] paying the expense of the experiments. The former adopted the plan of Bernouilli and Rumsey, using a centrifugal pump to force a jet of water from the stern; the latter used the screw. Livingston going to France as United States Minister, Barlow carried over the plans of the "Polacca," and Roosevelt's friends state that a boat built by them, in conjunction with Fulton, was a "sister-ship" to that vessel. In 1798, Roosevelt patented a double engine, having cranks set at right angles. As late as 1814 he received a patent for a steam-vessel, fitted with paddle-wheels having adjustable floats. His boat of 1798 is stated by some writers to have been made by him on joint account of himself, Livingston, and Stevens. Roosevelt, some years later, was again at work, associating himself with Fulton in the introduction of steam-navigation of the rivers of the West.[75] [74] "Encyclopædia Americana." [75] "A Lost Chapter in the History of the Steamboat," J. H. B. Latrobe, 1871. In 1798, the Legislature of New York passed a law giving Chancellor Livingston the exclusive right to steam-navigation in the waters of the State for a period of 20 years, _provided_ that he should succeed, within a twelve-month, in producing a boat that should steam four miles an hour. Livingston did not succeed in complying with the terms of the act, but, in 1803, he procured the reënactment of the law in favor of himself and Robert Fulton, who was then experimenting in France, after having, in England, watched the progress of steam-navigation there, and then taken a patent in this country. [Illustration: Robert Fulton.]