Dr. Duncan states, that, ‘_ammonia_ does not dissolve animal substances; it extinguishes flame; colors vegetable-blues green; is decomposed by being transmitted through a red hot tube, and, by the electric spark, into its constituent gases, and by oxygen, and atmosphoric air at a red heat; by oxy-muriatic acid, it is converted into water and hydrogen-gas. It is absorbed, without change, by porous bodies; it dissolves sulphur and phosphorus; and combines readily with water, in all its states. _Ammonia_ combines with the acids, forming neutral salts. It is formed during the putrefactive fermentation; and is commonly classed among the alkalies.’ My readers will see, at once, how wide a field is open for speculation! After quitting Johanna, which is the only island, in that cluster, whither European vessels ever intentionally resort, such as may be bound to Bombay usually make the great peninsula somewhere about Anjengo, pursuing their course up the western, or Malabar side; while those proceeding to Coast and Bay, (_i.e._ Madras and Bengal,) endeavor to get a sight of Dondra-Head, which determines both their latitude, and their longitude; thence they pass round the eastern side of the island of Ceylon, of which the shore is sufficiently bold to allow their keeping within two or three miles of the land with perfect safety, in regard to reefs or shoals; but this quarter being extremely subject to violent gales, that come on rather suddenly, or, at least, without much notice, and are known by the name of ‘white squalls,’ it is generally considered most prudent to keep a good offing. These white squalls invariably take place when the sky is free from clouds; but may sometimes be distinguished, as they approach, by the white spray raised from the water by the violence of the wind: so soon as that is discovered, all the small sails should be taken in, and the ship rendered as compact above as time may admit. The warning spray is too frequently unnoticed; and, even when perceived, is, for the most part, too close at hand to admit of much preparation. This insidious danger extends, more or less, from the south end of Madagascar up to the latitude of Tranquebar, being most prevalent to the southward of the Line, where the south-west trade wind prevails at all times.