[Illustrstion: PLATE II. FIG. 5.--BEARDMORE CEMENTED PLATE, 6-INCHES THICK, AFTER ATTACK BY 6-INCH SHOT. (From Brassey's Naval Annual, 1902 by permission) FIG 6.--KRUPP-CEMENTED PLATE, 3 INCHES THICK, AFTER ATTACK. (VICKERS, SONS & MAXIM) FIG. 7.--BACK OF A 6-INCH PLATE SHOWING ACTION OF CAPPED AND UNCAPPED PROJECTILES. FIG. 8.--BACK OF KRUPP PLATE 9.8 INCHES THICK, AFTER ATTACK, WITH CAPPED PROJECTILE. (KRUPP, MEPPEN.) (From Brassey's Naval Annual, by permission.)] Laws of Resistance. The laws governing the resistance of armour to perforation have been the subject of investigation for many years, and a considerable number of formulae have been put by means of which the thickness of armour perforable by any given projectile at any given striking velocity may be calculated. Although in some cases based on very different theoretical considerations, there is a general agreement among them as far as perforation proper is concerned, and Tresidder's formula for the perforation of wrought iron, t^2 = wv^3/dA, may be taken as typical. Here t represents the thickness perforable in inches, w the weight of the projectile in pounds, v its velocity in foot seconds, d its diameter in inches and A the constant given by log A = 8.8410. For the perforation of Harveyed or Krupp cemented armour by capped armour-piercing shot, this formula may be employed in conjunction with a suitable constant according to the nature of armour attacked. In the case of K. C. armour the formula becomes t^2 = wv^(3)/4dA. A useful rough rule is t/d = v/1900.