The secret, or rather one of the secrets of the Magi, has been revealed to us by one of the Fathers of the Church (Saint Hippolytus, it is thought), who has left, in a work entitled _Philosophumena_, which is designed to refute the doctrines of the pagans, a chapter on the illusions of their priests. According to him, the altars on which this miracle took place contained, instead of ashes, calcined lime and a large quantity of incense reduced to powder; and this would explain the unusual color of the ashes observed by Pausanias. The process, moreover, is excellent; for it is only necessary to throw a little water on the lime, with certain precautions, to develop a heat capable of setting on fire incense or any other material that is more readily combustible, such as sulphur and phosphorus. The same author points out still another means, and this consists in hiding firebrands in small bells that were afterward covered with shavings, the latter having previously been covered with a composition made of naphtha and bitumen (Greek fire). As may be seen, a very small movement sufficed to bring about combustion.--_A. De Rochas, in La Nature_. * * * * * TORPEDO BOATS. There are several kinds of torpedoes. The one which is most used in the French navy is called the "carried" torpedo (_torpille portée_), thus named because the torpedo boat literally _carries_ it right under the sides of the enemy's ship. It consists of a cartridge of about 20 kilogrammes of gun cotton, placed at the extremity of an iron rod, 12 meters in length, projecting in a downward direction from the fore part of the boat. The charge is fired by an electric spark by means of an apparatus placed in the lookout compartment. Our engraving represents an attack on an ironclad by means of one of these torpedoes. Under cover of darkness, the torpedo boat has been enabled to approach without being disabled by the projectiles from the revolving guns of the man-of-war, and has stopped suddenly and ignited the torpedo as soon as the latter came in contact with the enemy's hull.