An interesting engineering, achievement has recently been completed in India by spanning the river Indus with a double-deck steel cantilever bridge. The structure is described by the English correspondent of the SCIENTIFIC AMERICAN, and is also copiously illustrated. The improvements made in the materials used in building all kinds of machinery have, without doubt, been greater in the past few years than in any preceding period. E. F. Lake reviews the entire state of the art. Sir Oliver Lodge summarizes the present methods of tuning in wireless telegraphy. Some practical notes on etching are published. The attempts which have been made to produce synthetical camphor are reviewed. The geological formation of the Klondike is discussed by Dr. Willis Eugene Everette. B. M. Underhill contributes, a splendid rsum of the evolution of the horse. The United States government has expressed its intention of using military balloons for the army. Accordingly the Signal Corps has drawn up some specifications for a dirigible airship. For the interest of inventors these are published in the current SUPPLEMENT, No. 1669.