[Illustration: DIAGRAM SHOWING THE MAIN FEATURES OF THE SPHERICAL BALLOON]
The accompanying diagram gives a very good idea of the main features of the spherical balloon. The envelope is usually made of strong cotton diagonal cloth, cut in pear shaped gores and varnished with a solution of rubber in order to prevent the gas from leaking through. At the bottom it ends in the long _neck_,--through this the balloon is inflated by joining it securely to a gas pipe which leads to the main supply of gas. Over the envelope there is spread a strong _net_ made of heavy cord. From the net hang the stout _leading lines_. The leading lines in turn are attached to a strong wooden _hoop_, and from this hoop the car is suspended by ropes which are called _car lines_. The cords that connect with the upper and lower valves and the ripping panel hang down into the car and may be operated by the occupants, or crew.
Unless the balloon is held captive it is supplied also with a _trail rope_. This is a very heavy cable which is allowed to hang down from the car during an ascent. When descending, as the trail rope reaches the ground the balloon is relieved of a portion of its weight and becomes more buoyant. This makes its descent more gradual, for as it is relieved of one pound of weight of the dragging trail rope, it gains a slight tendency to rise again which counteracts the severity of its downward motion. The free balloon also has a _grapnel_ or anchor for use in landing.
The _car_ or _basket_ of the balloon is usually made of woven willow and bamboo, which insures strength and lightness.
This brief description of the spherical balloon is intended to give the reader an idea of the essential features of any balloon. In modern warfare the captive balloon has proved its usefulness for purposes of observation, but the old spherical type is passing out. Balloons of many shapes and sizes, all designed for greater stability, are taking its place. Among these the "kite" or "sausage" balloon is by far the best known. Partly a kite and partly a balloon, with its long sausage-shaped body, its air-rudder or small steering ballonet attached to its stern, it possesses considerable "steadiness" in the air.