The house should be big enough to allow room for a table and some chairs, stools, or benches, and the roof be so arranged that the tallest boy in the crowd may stand erect, with no fear of bumping his head. The furniture must be placed inside the frame as soon as the floor is laid, because after the house is finished the entrance is too small to admit the passage of any object of more bulk than a creeping boy. The hardest work is digging the foundation in the hillside, but if six or seven boys take a hand at this, “for the fun of the thing,” the work is soon done. [Illustration: FIG. 76.--Cross-Section of Excavation.] [Illustration: Bank Swallows at Work.] A Cross-Section is a picture showing how half an object looks. Fig. 76 is a cross-section of the excavation shown in Fig. 76a. The latter shows the finished foundation. [Illustration: FIG. 76a.--The Excavation.] In Fig. 79 a cross-section of the earth-bank and The Boys’ Underground Club-House is given, affording an idea of the proper proportions of the cave. When the foundation is entirely finished, collect your building material. If you have New Lumber, use it; if not, use old lumber, and if you are building in the woods the house may be built of logs and roofed with poles, covered with bark and boughs. The better the material the stronger will be the house. Secure some good sound planks and a supply of long strips two inches thick and four inches wide. Use two-by-fours for the frame of the house. To give a Pitch to the Roof, to allow the water which filters through the dirt above to drain off at the eaves, make the rear posts, A, B and C, D (Fig. 77), exactly equal in length, but considerably longer than E, F and G, H, as in Fig. 79. To add strength, erect another post midway between A, B and C, D. Framing. Cut the sticks A, C and B, D exactly equal in length and nail them to the uprights A, B and C, D, as in Fig. 77, using one nail at each corner; this will adjust the frame and make the four corners square, after which you may secure them in position by diagonal pieces similar to those shown on the end, A, E, B, F, Fig. 77. The corners may then be nailed. In nailing a temporary piece it is only necessary to drive the nails far enough to hold for the time. Next make the frame E, G, H, F, and in the middle of this frame nail on the two door-jambs I, J, and K, L. While some of the boys hold the front and rear frames in an upright position and the proper distance apart, others can nail on diagonals at the two ends, and, after all is square and plumb, the two string-pieces, A, E and C, G, may be securely nailed in place, and the rafter M, O nailed to M, N and O, P. This finishes the framework proper, for the club-house. Passageway.