The heads of the Kaffir’s spears are extremely variable in form, some being a mere spike, but the generality being blade shaped. Very few are barbed, and the ordinary shape is that which is seen several times in the illustration on page 103. Still, wherever the blade is adopted, it has always one peculiarity of structure, whether it be plain or barbed. A raised ridge passes along the centre, and the blade is convex on one side of the ridge, and concave on the other. The reason of this curious structure seems to be twofold. In the first place, it is possible that this structure of the blade acts much as the feathers of an arrow, or the spiral groove on the rifle balls invented by Dr. Croft, and which can be used in smooth bore barrels. Colonel Lane Fox finds that if a thread be tied to the point of an assagai, and the weapon be thrown with great care, so that no revolving force is given by the thrower, the thread is found spirally twisted round the head and shaft by the time that the weapon has touched the ground. That certainly seems to be one reason for the form. Another reason is, that a blade thus shaped can be sharpened very easily, when it becomes blunt. Nothing is needed but to take a flint, or even the back of a common knife, and scrape it along the edge, and, if properly done, a single such scrape will sharpen the weapon afresh. The head is always made of soft iron, and so yields easily to the sharpening process. The reader may remember that the harpoons which we use for whale hunting are always made of the softest iron; were they made of steel, the first furious tug of the whale might snap them, while, if they were to become blunt, they could not be sharpened without much trouble and hard work at the grindstone. Setting aside the two questions of rotatory motion and convenience of sharpening, it is possible that the peculiar structure of the blade may be owing to the fact that such a structure would produce the greatest amount of strength with the least amount of material. The sword bayonet of the Chassepot rifle is made on a similar principle. Whether the Kaffir is aware of this principle and forges his spear head in accordance with it, is another point. The reader, better informed than the Kaffir, may perhaps remember that the identical principle is carried out in the “corrugated” iron, now in such general use for buildings, roofs, and similar purposes.