"How?" asked his companions in one breath
"By this," replied the sub indicating the wristlet compass. "You hang on here. I won't be long."
"Be careful, then," said the A.P.
"Trust me for that," answered Barcroft cheerfully. "Lie low and keep a sharp look out."
On either side of the fence was a belt of reeds and coarse grass. In ordinary circumstances its height would be five or six feet, but the wind and rain had beaten down the reeds considerably. In places the tangle of grass was almost flat, and, combined with the slippery soil, formed a trap for the unwary.
"H'm! a fair amount of traffic on either side of the fence," commented Barcroft as he arrived upon the scene of his investigations. "They've had sentries patrolling up and down, but evidently they don't like the weather."
Kneeling in the slime the flight-sub unbuckled the strap that secured the little spirit compass to his wrist, then cautiously he held the delicate instrument towards the lowermost wire.
The needle was unaffected, even though he brought the compass close enough to risk a short circuit should the wire be highly charged with electricity. Three parallel wires he tested with similar results. At the fourth, which was about three feet from the ground, the needle oscillated. Whether it was owing to the deviating effect of an electric current or that he had unintentionally jogged the compass Barcroft could not decide. Withdrawing the instrument he waited for the sensitive index to come to rest.
"Dash it all!" he ejaculated as he resumed his investigations. "That wire is charged. It will mean a fine old job getting through this fence. Might squeeze through under the lowermost one if it could be prised up. But supposing the electrified wire isn't always the fourth from the ground: what then? I'll apply another test further along."
So intent was the flight-sub in his work that he failed to hear the faint sound of footsteps stealthily approaching through the squelching mud. Entirely at a disadvantage since he was crouching on his knees, Barcroft was most disgustedly surprised to hear a guttural exclamation, the form of which left no doubt as to the nationality of the speaker.