Yet as this artwork evolved and developed the Zeppelin began to diminish, and an interest grew instead for the coal-gas generated hydrogen that was trapped inside the airship´s hulking frame. Though I had some idea of the importance of coal in driving forward modern technological development, I was nonetheless struck by the degree to which this material had helped to create these massive flying machines. It seems odd to me that coal, as a dense, ground-based substance should be responsible for these objects of the sky.