[8]. Phil. Trans. Abridged, by Lowthorp, vol. II. p. 180.
The compass, though long known, was imperfect and liable to many inconveniencies, till at length, by the ingenuity of Dr. Knight, it was greatly improved; and has since undergone a further emendation by Mr. Smeaton. The improvement consists in the shape and temper of the needle; in the discovery of proper means for restoring the loss of magnetism in a voyage; and, finally, in rendering it less subject to be influenced by the motions of the ship. These contrivances, though found too delicate always to sustain with impunity the rude shocks of a tempestuous sea, or the more violent stroke of lightning, are, however, the best that have been yet discovered. Therefore, as this improved compass is allowed to be superior to others, and is now generally used in the royal navy, it ought certainly to be provided for all merchant ships, particularly on long voyages.
Ship’s Rudder.
8. The power of the rudder being reducible to that of the lever, and oblique action of the water, the most advantageous angle made by the helm from the keel, mathematicians have fixed at 54° 44′. Euler recommends an obliquity somewhat less; and establishes this rule, that an obliquity of 48° will, in general, produce the most powerful effect; though experience testifies, that a ship steers tolerably well when the rudder makes an angle of only 35°.
A convenient substitute for the loss of a rudder has been invented by captain Pakenham, for which useful device the Society of Arts presented him with a gold medal. The method, being described at large in the Society’s Transactions, need not be repeated in this place.
Masts.
9. To the mechanical genius of captain Pakenham, the navy is also indebted for an easy, cheap, and expeditious, method of restoring a mast, when injured, or decayed, by simply inverting the mast and turning the heel to the head; of which the Society, in the 10th volume of their Transactions, have given a full description, illustrated with an engraving.
The sudden damage which masts frequently sustain from sea-storms and naval engagements, and which, in the ordinary way, require from six to eight weeks to refit, may thus, we are assured, be repaired within forty-eight hours; and that this method is equally applicable to all ships, from a first-rate, to the smallest merchantman—a matter of no small consequence on long voyages, or in time of war.
Nautical Apparatus.
10. A ship, properly equipped for a long voyage, ought to be provided with a complete set of nautical instruments, including an accurate thermometer, barometer, and time-piece. Also, a life-boat, cork jackets, cords, drags, buoys, and other implements for the prevention of drowning.