ON THE REGULATION OF HYDRAULIC FORCES. 249 



turned from the wind if the rudder were not made to project from the stern 

 in a contrary direction, and to present the surface of an inclined plane to 

 the water which glides along the keel, so as to preserve the ship, by means 

 of the pressure which it receives, in any direction that may be required for 

 her manoeuvres. Commonly, however, although the sails may be so 

 arranged that the principal force of the wind appears to be on the fore part 

 of the ship, the curvature of the sails, or some other cause, throws the pres- 

 sure further backwards, and the action of the rudder is necessary to prevent 

 the ship's head turning towards the wind. (Plate XXII. Fig. 295.) 



When a ship is steering in this manner on a side wind, the effect of the 

 wind has a natural tendency to overset her, and if she is too crank, that is, 

 deficient in stability, she cannot sail well, otherwise than directly before the 

 wind. The place of the centre of gravity, compared with that of the meta- 

 centre, or imaginary centre of pressure, determines the degree of stability, 

 and the most general way of increasing it is to lessen the weight of the 

 upper part and of the rigging of the vessel, to diminish her height, or to 

 increase her breadth, and to stow the ballast as low as possible in the hold. 

 Too little attention has frequently been paid to this subject, as well as to 

 many other departments of naval architecture ; and although mere theore- 

 tical investigations have hitherto been but of little service to the actual 

 practice of seamanship, yet it cannot be doubted that an attention to what 

 has already been discovered of the laws of hydrodynamics, as well as to the 

 principles of mechanics in general, must be of great advantage to the navi- 

 gator, in enabling him to derive from his own experience all the benefits 

 which a correct mode of reasoning is capable of procuring him. 



LECT. XXVII. ADDITIONAL AUTHORITIES. 



Force of Water. Segner, Exercitationes Hydraulics, 4to, Gott. 1747. J. A. 

 Euler, Enodatio Qusestionis de Molis, Gott. 1754. Lambert on Mills, Hist, et 

 Mem. de Berlin, 1755. On Water-wheels, ibid. 1755, pp. 49, 70, 82. Mallet on 

 do. Ph. Tr. 1767, pp. 57, 372. Borda on do. Hist. etMem. de Paris, 1767, p. 270, 

 H. 149. Bossut on do. ibid. 1769, pp. 288, 477, H. 121. Fabre, Essai sur la 

 Maniere la plus avantageuse de construire les Machines Hydrauliques, 4to, 1783. 

 Buchanan on Water-wheels, Ph. Mag. x 278 ; xi. 79. Essay on Millwork, 2 vols. 

 1823. L'Huillier sur rArtd'Employerl'Eaucomme Moteur des Roues, Paris, 1823. 



Force of Wind. Hooke on the Sails of Mills and Ships, Philosophical Collections, 

 No. 3, p. 61. Lahire on Windmills, Hist, et Mem. de Paris, ix. 96. Euler on 

 do. Nov. Com. Petr. vi. 41. Hist, et Mem. de Berlin, 1756, p. 165. Bourrier's 

 Horizontal Mill, Hist, et Mem. de Paris, 1762, H. 190. Maiziere's Windmill, ibid. 

 1767, H. 185. Coulomb on Windmills and the form of their Sails, ibid. 1781, 

 p. 65, H. 41. Repertory of Arts, iv. 12 ; vii. 6, ii. I. II. 13, Phil. Mag. iv. 174. See 

 also Leupold's Theatrum Hydraulicum, Bailey's Machines, Machines Approuvees, 

 Emerson's Mechanics, and Encyclep. Method, art. Meunier. 



Seamanship. John Bernoulli's Theory of the Manoeuvres of Ships, Hist, et 

 Mem. de Paris, 1714, H. 107. Pitot on do. ibid. 1731, H. 81. Bouguer, ibid. 

 1754, p. 342, H. 91 ; 1755, p. 355, 481, H. 83, 135. Clairaut, ibid. 1760, p. 171, 

 H. 141. Bouguer, de la Manoauvre des "Vaisseaux, 4to, 1757. Euler, Scientia 

 Navalis, 2 vols. 4to, Petrop. 1749. Theorie de la Man. des Vais., Pet. 1773. 

 Romme, Art de la Marine, 4 to, Paris, 1787. Hutchison's Seamanship, 4to, 1794. 

 Chapman on Canal Navigation, 4to, 1797. Bezout, Traite de Navigation, Paris. 

 1814. 



Naval Architecture. Meibomius de Triremium Fabrica, 4to, Amst. 1671. Du- 



