"That’s good. We’re practically helpless here. They’ve knocked the wall about with their field pieces from the breastwork, and smashed the machine gun. We couldn’t hold the wall any longer. The carbide has given out, so that we can’t make any more acetylene for the searchlight, and the track’s free for them now. I only hope that as they’ve forced the passage they won’t trouble us any more, but go straight ahead in the morning. They little suspect what’s in store for them!" "They may possibly leave us alone, but they’re hardly human if they don’t try a shot or two at the aeroplane, especially when they discover what has happened to their own." "What did happen to it, by the way?" Lawrence described the incidents of the manoeuvring up and down river, and the extraordinary scene at the turning-place. It was then that he and Bob argued about the cause of the final collapse, almost forgetting their actual circumstances in discussing the scientific problem. They were suddenly recalled to realities, however, by sounds from the opposite bank--the ringing clatter of horses’ hoofs and the rumble of wheels. "They’re moving their guns up," said Bob. "No doubt they’ve only been waiting for the dark. Listen! We shall soon know what they mean to do." Both chafed at their inability to impose any check upon the movement. Rifle fire from their few men would be ineffective in the darkness; it would moreover be a signal to the gunners to sweep the wall with shell. They were not long in doubt as to the enemy’s intentions. The noises ceased. It was clear that the Kalmucks were going to wreak vengeance upon the garrison of the mine before continuing their march up stream. Bob recalled the old military maxim: never leave an enemy in your rear. At dawn they would no doubt open fire from the guns placed exactly opposite the mine, and as soon as they discovered the aeroplane on its platform beyond the shoulder of the cliff they would smash it to atoms. "I’ve still a few bombs left," said Lawrence. "I might destroy their guns if I could only see them. Isn’t there enough acetylene for ten minutes’ light, Bob?" "Not for one, worse luck. You certainly can’t do anything in the dark. There’s just one chance, though." "What’s that?" "You could light a big fire on the buttress yonder. It might show just enough light for the purpose." "I’ll try it. I tell you what: I’ll fire the shed itself, with a lot of combustibles inside. We can easily build another afterwards if Endicott gets rid of the enemy." "We shan’t want to do that. If we’re alive to-morrow morning we shan’t think of staying here any longer." "Leave the mine, you mean?"