I've been wondering if it's possible for an airship to fly by passive means - specifically, no engines (steam or otherwise).
I'm thinking in terms of a world where lighter-than-air gas (and it's containment) is fairly readily available, but that hasn't discovered mechanised propulsion.
The problem is - if you're sailing in water, the water itself provides resistance, and allows you to move in a different direction to the wind. (Whilst you can't sail directly into the wind, you can sail pretty close in a modern yacht).
But I think you're effectively adrift if you're trying to do the same with an airship - and are carried wherever the wind blows, much like a hot air balloon - you've no steerage, and the only way you get to go somewhere different is if the winds at different altitudes are blowing a different direction.
Is there any way this is possible, or am I going to have to think in terms of perhaps solar (convection?) propulsion or magic?