He struck three notes at slow intervals.

For all the world, Peter said, he was like a telegraph operator calling up a station.
'Send the message in English,' said Peter.
'They may not understand it,' said the man.
'Then send it any way you like.

I trust you, for we are brothers.' After ten minutes the man ceased and listened.

From far away came the sound of a trench-gong, the kind of thing they used on the Western Front to give the gas-alarm.
'They say they will be ready,' he said.

'I cannot take down messages in the darkness, but they have given me the signal which means "Consent".' 'Come, that is pretty good,' said Peter.