_Framing Details._ Despite this, the builders of the Zeppelins have adhered to the original pencil shape with but slight modifications at the bow and stern, probably because that shape is much easier to build and assemble from standard girders. The form of girder employed is shown in Fig. 17, while the complete assembly of the frame is illustrated in Fig. 18. The girders form the longerons, or longitudinal beams, running the entire length of the rigid frame and supported at equidistant points by ring members built of similar girder sections. The fourth ring from the nose and each alternate ring after that are further braced by being trussed to the longitudinal beams around their entire circumferences, as shown in Fig. 18. The larger V-shaped truss at the bottom forms the gangway, which is now placed inside the envelope instead of being suspended beneath it, as formerly. This is done to eliminate the head resistance set up by the additional surface thus exposed. In the first instance in which this gangway was incorporated in the envelope, no provision was made for ventilation, and the ship was wrecked by a gas explosion. Regardless of how tight the fabric is made, gas is always oozing out through it to a greater or less extent. This fact is now met by providing ventilating shafts leading from the gangway to the upper surface of the envelope. Additional shafts through the envelope lead to gun platforms, forward, amidships, and aft, and are reached by aluminum ladders. [Illustration: Fig. 17. Trellis Type of Aluminum Girder used in Longitudinals of Zeppelin Frame] [Illustration: Fig. 18. Aluminum Frame Construction of Zeppelin Hull]