house, the shell from the gun will tend to hit the front wall, whereas the shell from the howitzer will tend to drop upon the roof. This tendency, combined with their difference in mobility, determines the choice of a gun or howitzer with which to attack a given target. It may be added that by still further reducing the range to be attained, say to a few hundred yards, a charge of only a few ounces need be employed, and a weapon produced, capable of being carried by a couple of men, yet still throwing a comparatively heavy shell. The German _Minenwerfers_ and our own trench-mortars are the representatives of this class. All these various types and sizes of ordnance (the word "gun" is a generic term that covers them all) employ two main types of projectile, shrapnel and high explosive. Shrapnel may be considered as a sort of shot gun fired from a rifled gun. It consists of a steel case filled with round bullets except for a chamber in the base containing a small quantity of powder. The head of the shell is fitted with a fuse which can be set to act at any given time after the gun is fired. This fuse ignites the powder in the base of the shell, which projects the bullets from the case in the form of a cone whose axis is the direction in which the shell is moving at the time. Shrapnel, therefore, depends for its effect upon the destructive power of the flying bullets. High-explosive projectiles consist of a very strong and heavy shell, entirely filled with a high-explosive compound, and fitted with a percussion fuse that acts when the shell strikes anything. The fuse ignites a primer which detonates the high-explosive charge, and the body of the shell splits up into pieces of various sizes which are hurled in all directions with considerable velocity. This type of shell has a double destructive power, that of the high explosive itself and of the flying fragments. The Germans employ a compromise in addition, known as "universal" shell, which may be described as a shrapnel with a high-explosive charge, which can be used with either a time or percussion fuse. They have also combined with the explosive charge of some of their projectiles a substance which on combustion produces an irritant gas with the property of attacking the eyes, and thereby making a position untenable, and have also added phosphorus to produce incendiary effects. It may be accepted as a general rule that howitzers employ only high explosive, guns both shrapnel and high explosive.