611 Reporter's Statement of the Case ram in large lengths, this being largely due to the tendency of a pile that is being driven to pull an adjacent pile down with it. The object of the present invention is to produce a pile which can be easily rolled like a pile with a sickleshaped cross section but which at the same time offers greater resistance to lateral bending stresses. Furthermore, a pile constructed according to the present invention, can be rammed in as readily as one having an S-shaped cross section. This is accomplished by making the piles of two parts of sickle-shaped cross section and joining these parts together so as to form an Sshaped pile before it is rammed in. The two sickleshaped pile elements are formed at their edges with interlocking members that are caused to interlock by the application of lateral forces. It has been found that bi-part piles produced in this manner have excellent ramming properties. Thus piles having a fullwave cross-section have two properties which render them superior to those which are provided with a halfwave cross-section. In the first place, the former has double the inertia of the latter. In the second place the resistance offered by the medium in which the piles are driven, is doubled for the former as compared to the latter while the sliding friction between a previously-driven pile and one in process of being driven, is substantially the same for piles of both types. It is in connection with these properties that the advantages to be derived by the hereinafter described method of making piles with cross-sections of compound curvature, will be apparent, I have found that a very advantageous form of bi-part pile is produced by providing the interlocking edges of the parts with projections or protuberances which assist the frictional forces at the joint in preventing the parts of the bi-part pile from being displaced relatively to each other during the ramming operation. 4. The patent in suit, Figs. 1 and 2, provides a unit of sickle-shaped metal a, one extremity of which indicated by c is an open claw, the other extremity or edge b is described as a protuberant part or rib. A complemental sickle-shaped pile member indicated in Fig. 2, on the right-hand side of this figure, by a, is shown in which the edge e is designed to grip the lateral rib b of the other pile member, and also engage the transverse projections d of the first mentioned pile member. This engagement of the two pile members a, Fig. 2, is not merely a frictional interlock, but is accomplished by hammering together the two parts with a pneumatic hammer or the application of other lateral force. The small arrows, shown in Fig. 2 at the point of interlock, indicate the direction and application of the extraneous force necessary to unite the two sickle-shaped half-wave sections of the completed full-wave pile. Fig. 4 shows the 611 Reporter's Statement of the Case claw c with the recess d at the edge of one pile section surrounding the projecting locking ribs d of the second pile section. In this figure 4 no external pressure has been applied; the two pile sections are not in interlocked or positive relationship. Turning to Fig. 3, which is a side view of the two half waves in locked relation, d indicates the projecting locking ribs on the left half-wave pile, e the edge of the complemental right-hand pile crimped over the locking ribs d, and the protuberant edge b of the left-hand pile section. 5. Engineers have long recognized the virtue of forming piles of oppositely disposed trough shapes or curved sections. Variously they are termed S-shaped, double-curved, or full-wave piles. Their properties are well known to those skilled in the art, and the advantages in their use as contrasted to piles presenting a flat or plane surface is a matter well understood. The superiority of the oppositely disposed sections or Sshaped piles lies in their increased resistance to lateral forces or their inherent ability to remain rigid and unbending when pressure is applied to one side of their faces. In the engineering nomenclature of this art of sheet piling the terms "section modulus," "neutral axis" are used to express certain physical characteristics of piles. "Section modulus" of a pile is simply a measurement of the ability of the particular pile to resist bending action. It is a measure of the stiffness of a pile to resist thrust or pressure at right angles to its vertical axis. This quality of stiffness or the amount of pressure necessary to bend the pile differs with each different design of pile, thus a pile with a high section modulus is more efficient and remains more nearly static than a pile of low section modulus, when the same lateral force is applied. A pile of twice the section modulus of another pile is twice as resistant to lateral force or in other words double the lateral force or pressure would be required to bend the former as the latter. 6. The consideration of and the determination of the section modulus of a beam, sheet pile, or any structural element is exceedingly important, as the load to be carried and with Reporter's Statement of the Case 93 C. Cls. stood by the beam or pile defines the degree of section modulus, i. e., the required strength of the element, to support the work load. This is elemental in engineering experience long prior to the date of the patent in suit. When sufficient lateral force is applied to a driven pile to bend the pile such bending will occur about the neutral axis of the pile structure. 7. An accepted definition of "neutral axis" of a structural section or pile section is "an axis which is passed through the structural section or any section would result in a balance of areas on one side of a neutral axis as against the area on the other side. In other words there would be a complete balance of weights along the line called the neutral axis.” To give proper "section modulus" to a pile of the type disclosed in the patent in suit and allied designs, as much material as is possible is placed on the outer sides of the two pile sections, taking a cross sectional view, such disposal of metal being as far as possible away from the neutral axis of the two pile sections. 8. In the patent in suit no specific mention is made of "section modulus" or "neutral axis," but such terms are ordinarily used in a multitude of engineering computations and are useful and well known as means of measuring and compiling material values and structural safety loads. CLAIMS IN ISSUE 9. All five claims of the patent in suit are declared upon; four are directed to a method of fabricating the structure, while the fifth is for an article of manufacture, i. e., a specific type of pile. They read as follows: 1. The method of constructing a metal pile having a full-wave cross-section, which method consists in separately forming complementary parts of said pile with oppositely curved half-wave cross-sections, and in rigidly uniting said parts along adjoining longitudinal edges thereof with the half-wave cross-sectioned parts extending in opposite directions from the rigid joint between the adjoining edges of said complementary parts. 2. The method of constructing a metal pile which method consists in separately rolling complementary parts of said pile with curved cross-sections, and in rigidly uniting one longitudinal edge of one of said parts 611 Reporter's Statement of the Case with one longitudinal edge of the other of said parts, the other longitudinal edges of said parts being presented outwardly in opposite directions with respect to the rigid longitudinal joint between said parts and with the curved cross-sections of said parts disposed on opposite sides of a common plane through said oppositely and outwardly presented other longitudinal edges. 3. The method of constructing a metal pile which method consists in separately rolling complementary parts of said pile with oppositely curved cross-sections, and with one edge of each of said complementary parts adapted to interlock with one edge of the other of said complementary parts, in interlocking said edges with said complementary parts extending oppositely with respect to said interlocking edges and with said curved cross-sections disposed on opposite sides of a common plane, and finally in rigidly uniting said interlocking edges. 4. The method of constructing a metal pile, which method consists in separately rolling full length partsections of the desired pile with half-wave cross-sections, in arranging said part-sections edge to edge along one edge of each part-section and with the other edge of each part-section presented away from the other part-section, said half-wave cross-sections being disposed on opposite sides of a plane common to the opposite edges of both of said part-sections to form a full wave cross-section of compound curvature, and finally in rigidly uniting the adjoining edges of said part-sections to form a pile having full-wave cross-section. 5. As an article of manufacture, a metal pile comprising two complementary parts, said parts being rolled separately to provide them with trough-shaped crosssections and rigidly united along adjoining longitudinal edges with said complementary parts presented in opposite directions from the rigid joint therebetween and having the trough-shaped cross-sections of said complementary parts respectively disposed on opposite sides of a common longitudinal plane through said metal pile. 10. The type and construction of the sheet piling used by the United States Government and charged to be an infringement of the patent in suit, is exemplified by the sheet piling installed at the Boston Army Supply Base. This piling was trough-shaped, in two sections, which have at their outer extremities or edges a claw-shaped portion adapted to engage the edges of similar trough-shaped sec |