A zeppelin could use compressor tanks to control its buoyancy in an exactly analagous way. Lots of details on how the problem was handled in practice here: ht

A zeppelin could use compressor tanks to control its buoyancy in an exactly analagous way. Lots of details on how the problem was handled in practice here: http://en.wikipedia.org/wiki/Buoyancy_compensator_(aviation) http://en.wikipedia.org/wiki/Buoyancy_compensator_(aviation)