[29] 1. The middle beam. 2. The end with iron bars wherein the strength of the ship lyeth both ends alike. 3. Rudder of the ship. 4. The keel. 5. Iron bolts with screws. 6. Depth of the inner beam. 7. The wheel that goeth round it hath its motion. 8. The scuttles or hatchways. 9. The gallery where they walk. [30] “Specifications relating to Marine Propulsion,” Woodcroft, Part I. p. 29. [31] Woodcroft, Part I. p. 51; and see Drawings, “Repository of Arts,” vol. i. (second series), p. 11. [32] “He was a foolish man,” says Dr. Arnott, “who thought he had found the means of commanding always a fair wind for his pleasure boat by erecting an immense bellows in the stern. The bellows and the sails acted against each other, and there was no motion: indeed, in a perfect calm, there would be a little backward motion, because the sail would not catch all the wind from the bellows.”—Arnott, “Elements of Physics,” p. 120. [33] “Specifications of Marine Propulsion,” Woodcroft, vol. i. pp. 16 and 17. [34] Papin was driven from France by the revocation of the Edict of Nantes, and was associated with Robert Boyle in many of his experiments on the air-pump—he was elected F.R.S. in 1681, and was for a time, the secretary of the society. He was invited to Germany by the Landgrave of Hesse, was some years Professor of Mathematics at Marburg and died there, 1710; he seems the first to have clearly discerned the necessity of the vacuum under the cylinder, and that the pressure of the atmosphere alone is enormous. (A cylinder 1 foot in diameter, has a surface of 113 square inches, hence, the atmospheric pressure in it is 113 ⨉ 15 = 1695 lbs.). Papin first proposed to exhaust the air by pumps, and in 1687 laid this plan before the Royal Society; but such a plan would only have been a transference of power, the effect being the same in character as that of lifting the water to the water-wheel. His most important invention was that of a method of producing a vacuum by the condensation of steam—the reversal, in fact, of the process of the previous machines of De Caus and Lord Worcester. He drew the inference that, if water in its conversion into steam swelled many hundred times, it must follow that steam reconverted into water would shrink into its primitive dimensions. He was also the first to suggest the safety-valve, but he did not, strange to say, apply it to the machine subsequently invented. It has been asserted, though not proved, by some writers that Papin derived many of his ideas from Otto von Guericke, who had invented an air-pump as early as 1654. [35] The “Miners’ Friend,” &c. A paper published by Savery in 1702.