Should any person possessing the opportunity and means, wish to try the experiment, I would advise them to get a barrel of 4-1/2 feet long, 8 bore, to carry a 2 oz. ball, and of a weight to allow of extending the explosion up to 30 drs. of powder; they would then obtain the extent of force I have suggested. There is a certain point to be strictly observed: see that the plate you use is perfectly sound; for if laminated, or composed of various plates not firmly welded and attached, the experiment would be imperfect, as there would be an uneven vibration created, and acting as the hammer does when held against the point of the nail while driving it in, clinches the point, so does the substance in the portions of plate prevent a perforation. An ounce ball, suspended against the back of the pendulum, by the jar or blow it receives and communicates, completely prevents the effect, and the ball is flattened, instead of perforating the object struck: so is it if you place a 1/4-inch plate against any support; it thus has the power of perfectly resisting the force of the ball, though fired with considerably more power than is requisite under other circumstances. The effect appears to be chiefly mechanical; the outer fibres are driven in upon those behind them with such quickness that they lose cohesion, or are condensed quicker than the waves of vibration travel, thus giving them no means of communicating the vibration. But when punched, the rapidity of their motion produces in the metal a sound of the most intense vivacity, which plays upon the ear for a considerable period, with rather a pleasant effect. Lead alone is capable of being used in this experiment; except, of course, the precious metals, which it would not be _convenient_ to use. Even an adulteration of the slightest quantity of solder is sufficient to prevent the result which lead, pure, will invariably give. Lead projected against lead, if sufficiently thick, cannot perforate, but the lesser portion becomes flattened; a cast-iron ball fired against lead, with a certain velocity, is broken into pieces, affecting the lead comparatively little: showing beautifully the peculiarity of dense incompressible bodies to resist most effectually the greater the velocity with which they are struck. Water will, if struck very sharply with the flat of a sword, act against the blow in a way to splinter the blade into pieces. The greater the velocity with which a ball is fired into water, the less the depth of penetration; thus showing clearly the many excellent properties of dense incompressible bodies as projectiles, and proving the objection that lead is too soft for artillery to be without a foundation, and only entertained from a want of knowledge of its nature. A point of great importance was exemplified during these experiments; and as the question has lately given rise to considerable discussion, it will be well that the facts should be stated.