The first form (fig. 118) is the wedge that would be produced by taking for base the dorsal thickness of an ordinary blade, and by continuing it in an even line to the apex of the triangle—the point. The two sides meet at an angle of nine degrees; consequently the edge lacks the thickness, weight, and strength necessary for every cutting tool. For soft substances it should range from ten to twenty degrees, as in the common dinner knife. An angle of twenty-five to thirty-five degrees, being the best for wood-working, is found in the carpenter’s plane and chisel. For cutting bone the obtuseness rises to forty degrees, and even to ninety; the latter being the fittest for shearing metals, and the former for Sword-blades, which must expect to meet with hard substances. But even an angle of forty degrees will be ineffectual upon a thick head, unless the cut be absolutely true. No. 2 illustrates the angle of resistance (forty degrees) and the entering angle (ninety degrees). No. 3 shows that the true wedge of forty degrees is too thick and heavy for use, requiring some contrivance for lightening the blade, while preserving the necessary angle of resistance. The remaining sections display the principal modes of effecting this object. In Nos. 4 and 6 the angle is carried in a curved and bulging line, thus giving the section a bi-convex form. When the back or base is flat this is the Persian and Khorásáni, vulgarly called the ‘Damascus blade.’ When baseless and two-edged it is the old ‘Toledo’ rapier—two shallow-crowned arches meeting (3_a_, fig. 124). In both cases the weapon is strong, but somewhat overweighted. In the next shapes (Nos. 5 and 7), the two sides are cut away to a flat surface and represent the ‘Talwár’ of India. When this flat surface is hollowed, as by the black lines of No. 5 (compare No. 8), we have the bi-concave section, as opposed to the bi-convex. This hollowing of the wedge into two broad grooves from the angle of resistance is one of the forms assumed by the English ‘regulation’ Sword: it was considered the lightest for a given breadth and thickness, but it is by no means the strongest, and there are sundry technical objections to it.