One, a steamer, is being nursed by means of a gas tube to keep the fire-box warm.
The mobility of the gas tube at m'' is of advantage in this operation.
The air tube, l, passes into the gas tube and is continued concentrically within the latter.
To keep ashes and dust out of the gas tube, lumps of charcoal are heaped up to the height of the top of the flue.
Might be one of those gas-discharge curves, if the gas tube happened to be defective.
Here was the logical place to set the gas tube, nose pointed ahead.
Only one of us must risk taking the gas tube any nearer the enemy.