Young Stevens began working in his father's machine-shop in 1804 or 1805, when a mere boy, and thus acquired at a very early age that familiarity with practical details of work and of business which is essential to perfect success. It was he who introduced the now common "hollow water-line" in the Ph[oe]nix, and thus anticipated the claims of the builders of the once famous "Baltimore clippers," and of the inventors of the "wave-line" form of vessels. In the same vessel he adopted a feathering paddle-wheel and the guard-beam now universally seen in our river steamboats. As usually constructed, this arrangement of float is as shown in Fig. 87. The rods, _F F_, connect the eccentrically-set collar, _G_, carried on _H_, a pin mounted on the paddle-beam outside the wheel, or an eccentric secured to the vessel, with the short arms, _D D_, by which the paddles are turned upon the pins, _E E_. _A_ is the centre of the paddle-wheel, and _C C_ are arms. Circular hoops, or bands, connect all of the arms, each of which carries a float. They are all thus tied together, forming a very firm and powerful combination to resist external forces. [Illustration: FIG. 87.--The Feathering Paddle-Wheel.] The steamboat Philadelphia was built in the year 1813, and the young naval architect took advantage of the opportunity to introduce several new devices, including screw-bolts in place of tree-nails, and diagonal knees of wood and of iron. Two years later he altered the engines of this boat, and arranged them to work steam expansively. A little later he commenced using anthracite coal, which had been discovered in 1791 by Philip Ginter, and introduced at Wilkesbarre, Pa., in the smith-shops, some years before the Revolution. It had been used in a peculiar grate devised by Judge Fell, of that town, in 1808. Oliver Evans also had used it in stoves even earlier than the latter date, and at about the same time it had been used in the blast-furnace[81] at Kingston. Stevens was the first of whom we have record who was thoroughly successful in using, as a steam-coal, the new and almost unmanageable fuel. He fitted up the boiler of the steamboat Passaic for it in 1818, and adopted anthracite as a steaming-coal. He used it in a cupola-furnace in the same year, and its use then rapidly became general in the Eastern States. [81] Bishop.