There is also a valve in the neck of the balloon which opens automatically when the pressure becomes too great, or which can be operated by a cord. The Romance of Aircraft - Σελίδα 16 των Laurence Yard Smith - 1919 - 264 σελίδες Πλήρης προβολή - Σχετικά με αυτό το βιβλίο
...jerked, the fabric is torn open, and the gas escapes. This enables the aeronaut to make a quick descent. There is also a valve in the neck of the balloon, which is opened automatically and prevents the balloon from bursting if the pressure inside becomes too great....