96 PRINCE ROBERT'S BOAT. is generated being its only objection; for it was found by succeeding experimenters, that the materials which composed the fire-place, as well as the fuel, disappeared before the energy of the "little volcano." Papin apparently not being aware that this current would continue in the descending direction, hinted the advantage to be derived from forcing the air upon the fuel; and hazarded the conjecture, that a double velocity being given to it the heat produced should be four times greater.* ; This fine arrangement and combination of parts was equalled by the purposes to which the ingenious Frenchman suggested it might be applied. The object he had first in view was the draining of mines; he said it might also throw bombs and above all, that it might propel a vessel against the wind, and supersede the labour of rowers and galley-slaves in ports and havens; and thus allowing these persons to be employed on their proper element, the sea, instead of reposing the greater part of their time in port or on shore.t In discussing the advantages of his mechanism over human power in maritime movements, the mechanical difficulties which were to be overcome before his project could be practicable were observed but to be ingeniously obviated. He was quite aware that the rectilineal movement of the piston in his cylinder could not be effectively applied to a mechanism like a common oar. During his residence in England he had witnessed an interesting experiment made on the Thames, in which a boat, constructed from the design of the Prince Palatine Robert, was fitted with P. 51, ibid. * P. 63, ibid. revolving oars, or paddles attached to the two ends of a long axle going across the boat, and which received its motion from a trundle working in a wheel turned round by horses. The velocity with which this horse-boat was impelled was so great, that it left the king's barge, manned with sixteen rowers, far astern in the race of trial.* The use of wheels for oars is very ancient. In some very ancient MSS. extant in the King of France's library, it is said the boats, by which the Roman army under Claudius Caudex was transported into Sicily, were propelled by wheels moved by oxen. And in many old military treatises the substitution of wheels for oars is mentioned. Robert Valturius gives a view of two gallies moved by wheels instead of oars: the first diagram shows five wheels on each side of the vessel; each pair are connected by a sepa rate axle running across the boat, this axle is formed like a crank in the middle of its length, and the five axles are connected together by a rod, or a rope, so that all their movements are simultaneous. The second diagram has one wheel at each side of the galley; these are also connected by an axle running across the boat, as shown in figure: he gives no details, but he merely mentions, that the velocity of these boats will be greater than if they were propelled by oars. De Re Militari, lib. xi. p. 2. Veronæ, 1472. Pancirollus, a celebrated professor at Padua, in 1587, saw an ancient bas-relief, which represented a galley with three wheels on each side of a boat turned by three pair of oxen. And he observes, that they would have a greater velocity than the swiftest three-decked gallies. Res Memorabiles, p. 127. Ambergæ, 1599. An old English writer on military subjects says: "And furthermore you may make a boate to go without oares or sayle, by the placing of certain wheeles on the outside of the boat, in that sort, that the armes of the wheels may go into the water, and so turning the wheels by some provision, and so the wheels shall make the boate goe." Invention, or Devises, by William Bourne, p. 15. London, 1578. Edmund Bushnel, a shipwright, describes "a mode of rowing ships by heaving at a capstan, useful in any ships becalmed." He connected the oars on each side of the vessel together, and he gave them the alternate backward and forward movement, by attaching the connecting pieces to ropes which were wound and unwound by the capstan. Compleat Shipwright, p. 56, fourth edit. 1678. K 98 ROTARY MOTION. This was the mechanism he wanted; but before he could avail himself of so fine a thought, it was necessary that he should contrive to convert the alternate motion of his piston-rod into a continuous rotary one. To one so well acquainted with mechanical contrivances there could be little difficulty in doing this; watchmakers practised various modes of converting the one motion into the other, and the one which occurred to Papin was suggested by clockwork mechanism. A rack, b, was placed on the piston-rod, working into a pinion, a, fastened on the axle of the revolving paddles. He employed two or three steam cylinders, and when the piston of the one was ascending that of the other was working downwards, and as this would give contrary motions, one was detached while the other was in action, and by this means his motion could be made continuous and tolerably regular. A horse "tow-vessel" was used at Chatham, in 1682. It was constructed with a wheel on each side of the vessel, connected by an axle going across the boat, and the paddles were made to revolve by horses moving a wheel turning by a trundle fixed on the axle. It drew but four and a half feet of water, and towed the greatest ships by the help of four, six, or eight horses: the wheels were permanently fas tened to the side of the boat; the capstan, to which the horses were yoked, was not that of the boat. Savery's Navigation Improved, p. 13. London, 1693. This, probably, is the identical vessel mentioned in the text. |