The cast-steel armour made by Hadfield has already been alluded to. That made by Krupp (the only other maker at present of this class of armour) is of face-hardened nickel steel. A 5.9-in. plate of this material tried in 1902 had a figure of merit of more than 2.2 against uncapped 5.9-in. armour-piercing projectiles of 112 lb. in weight. The main advantage of cast armour is that it is well adapted to armoured structures of complicated design and of varying thickness, which it would be difficult or impossible to forge in one piece. It should also be cheaper than forged armour, and, should time be a consideration, could probably be turned out more quickly; on the other hand, it is improbable that heavy castings such as would be required could be as regular in quality and as free from flaws as is possible when forged material is used, and it is unlikely that the average resistance to attack of cast-steel armour will ever be equal to that of the best forged steel. Defence against small-arms. Of recent years there has been a considerable demand for thin steel plating proof against small-arm bullets at close ranges. This class of steel is used for field-gun shields and for sap shields, to afford cover for men in field-works, for armoured trains, motor-cars and ambulances, and also very largely for armouring shallow-draught river-gunboats. Holtzer made chrome steel breastplates in 1890, 0.158 in. of which was proof against the 0.43-in. hard lead bullet of the Gras rifle at 10 metres range, while 0.236 in. was proof against the 0.32 in. 231-grain Lebel bullet at the same distance, the striking velocities being approximately 1490 and 2070 ft. per second respectively. The bullet-proof steel made by Messrs Cammell, Laird & Co. in Great Britain may be taken as typical of that produced by the best modern manufacturers. It is proof against the 215-grain Lee-Enfield bullet of 0.303 in. calibre striking directly, as under: Range. Thickness of Plate. Striking Velocity. 10 yards 0.187 inch 2050 f.s. 100 " 0.167 " 1865 " 560 " 0.080 " 1080 " The weight of the 0.08 in. plating is only 3.2 lb. per sq. ft. The material is stated to be readily adaptable to the ordinary operation of bending, machining, drilling, &c., and is thus very suitable for the purposes indicated above. (W. E. E.)