Thermometer.
From the result of three successive voyages from Europe to America, captain Williams, under the direction of Dr. Franklin, found the temperature of the main ocean, out of soundings, at least ten degrees warmer than in shallower water near the coast. Hence the thermometer may serve a new and important purpose in pointing out the near approach to shore; also, in detecting latent rocks, or banks of sand or coral, concealed under water. Is the decrease of temperature owing to these solid bodies acting as conductors, and thus conveying off the heat?
Nautical Time-piece.
A curious and unsuspected cause of inaccuracy in watches, or time-pieces, has lately been discovered by an ingenious artist, which well deserves notice. The balance, being made of steel, is very liable to acquire a polarity, which disturbs the regularity of its movement, according as the watch happens to be placed North and South, or in the vicinity of a knife, a key, or other steel utensil. On trying a variety of steel balances, by floating them on cork, placed on the surface of water, Mr. Varley could scarcely select one that did not betray some sign of polarity; nor can this be easily prevented, but by substituting a balance of gold, or some other metal. May not this be one reason why that grand desideratum, a perfectly correct time-piece for discovering the longitude at sea, has not yet been produced?
To prevent accidents during long voyages, the Transactions of the Royal Society of London suggest many important hints; which, however, for the sake of brevity, must be omitted, by referring the reader to the respective passages, viz.
1. To preserve vessels from the worm, by a more cheap and durable method than that of sheathing; also, to prevent leakage from the same cause.—See Phil. Trans. vol. VIII. p. 6192.—Vol. XLIII. p. 370.
2. To preserve the health and lives of men crowded in slave ships, and transports, by ventilators, and other means.—Vols. XLIV, and XLVII. p. 211.
3. To measure the ship’s way more correctly than by the log, &c.—Vols. XXXIII, and XXXVIII.
Also, a still later method, with improvements. See Memoirs of the American Philosophical Society, vol. II.