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of the characters of bottoms and of the existence of any sediment or deposit; of the sources of sediment and the means of turning it away; the examination of the effects of ice on the beds; and the determination of the density of the water, with special reference to the displacement of salt water by fresh water from adjacent streams and rivers. The plan of the work was to make the investigation exhaustive over a limited area, and extend it afterward as circumstances should permit. The results are given in the present memoir.

Explosive Materials. By M. P. E. Berthelot. Translated from the French by Marcus Benjamin. New York: D. Van Nostrand. (Science Series.) 1883. Pp. 180. Price, 50 cents.

In these lectures M. Berthelot has summed up the results of his researches upon explosives, and indicated the theory of their action which they seem to him to warrant. He is mainly concerned in considering how an explosive is set in operation by means of shock, and reaches the conclusion that in all cases, whether the explosive influence be propagated from particle to particle of an explosive, or from one explosive body to another, not in contact with it, the action consists in the transformation of the energy of the shock into heat. Before an explosion can occur, some portion of the substance must be raised to the temperature necessary for the chemical reaction between its constituents. That this temperature should be reached, it is necessary that the impact be sudden, as otherwise the transformation into heat will take place so slowly that this heat will be distributed through too great a mass of material to raise its temperature to the requisite point. The explosion of one particle of the substance produces a sudden pressure, the energy of which, transformed into heat, causes the next particle to explode, and so on, the disturbance being thus propagated through the entire mass of the explosive. M. Berthelot rejects the synchronous theory of explosions by influence—where a body is exploded by another at a distance—of Abel, holding that the theory of transformation of mechanical energy into heat, and the retransformation of this into mechanical energy, is competent to explain all the phenomena. In discussing the conditions of maximum effect in explosion, he points out the reason for the extremely low velocity of propagation of the explosive wave in gases, obtained by Bunsen, and shows that this in reality moves with great rapidity.

Mr. Benjamin's translation appears to be accurate, and, despite occasional roughness, is fairly well done. The volume contains also a short historical sketch of gunpowder, translated from the German of Karl Braun, and a bibliography of works on explosives.

The Ores of Leadville and their Modes of Occurrence, as illustrated in the Morning and Evening Star Mines. With a Chapter on the Methods of their Extraction as practiced at those Mines. By Louis D. Ricketts, B. S., Princeton, N. J. Pp. 68, with Six Plates.

The author, in order to comply with the requirements of the W. S. Ward Fellowship in Economic Geology, in connection with Princeton College, devoted four months at Leadville to the study of the ores and their modes of occurrence, and to the extraction of the ores in the mines named in the title we have cited. The result of this study is given in the present paper, of which the first part considers the scientific and the second part the practical side.

J. A. Berly's British, American, and Continental Electrical Directory and Advertiser. London: William Dawson & Sons; New York: George Cumming, 219 East Eighteenth Street. Pp. 664. Price, $2.50.

This volume, which embodies a record of all the industries directly or indirectly connected with electricity and magnetism, and the names and addresses of manufacturers in England, the United States, Canada, and the European Continent, is a valuable book of reference for all persons interested in electrical art. The increased size and importance of this, the second edition, over the volume published a year previously, which was chiefly limited to England, is one of many signs of the rapidly expanding development of the applications of electricity. Another similar sign is afforded by the variety of trades some of them appearing at first sight only very remotely related to electricity that have been included within its scope. The relation is nevertheless real, for all these trades have been brought in to