Dick pulled out his telescope.
“A big black square,” he said. “Up on end. Like a diamond.”
“It’s a signal,” said Dorothea.
“But how are we to know what it means?” said Dick.
There was a hail in the distance, and they saw John, alone, scrambling through the dead bracken on the ridge beyond the tarn. Anybody could see that he was in a hurry as he came to the ice, stamped on it once or twice and then came quickly across, walking and sliding. He had a knapsack on his back and was carrying a big, awkward white parcel. Dick and Dorothea went to meet him as he came racing up the slope.
“How does our signal look from the barn?” he panted. “Can you see what it is?”
He turned and looked back to Holly Howe.
“Not half bad,” he said.
“But what does it mean?” asked Dick.
“We haven’t decided yet,” said John. “Let’s try how it works from this end. I stuck some whitewash on these to make them show against the dark stone. Can I go up?”
“Of course,” said Dorothea.
“Let’s,” said Dick.
They went up the steps and into the loft where Dorothea and Dick had shivered two nights before while sending out their flashes to catch the attention of the Martians. John propped his parcel against the wall, where Dick examined it carefully. It was simply two big flat pieces of wood, one of them a triangle and the other a square.
“Look out!” said John. “The whitewash is only just drying!”
“Have you lost something?” said Dorothea, seeing John looking this way and that about the loft.
“I just want something for a hammer,” said John. He ran down the steps again, and came back with a biggish stone.
“This’ll do,” he said, trying it in his hand, and went to the big window. He stood there on the sill, holding to the wall with his right hand and reaching round it and as high up it as he could with his left. He found a crack between the stones, pushed into it a big nail that he fished out of his pocket, battered it firmly in with his stone hammer, and gave it a last knock from below to make it turn upwards.
“But I won’t be able to reach as high as that,” said Dick, who guessed what he was doing.
“Half a minute,” said John. “You won’t have to.”
Out of his pocket he brought a ball of string, another large nail, some double hooks of thick fencing wire, and a big brass curtain ring.
Dick and Dorothea watched, open-mouthed.
John threaded the string through the curtain ring, reached round the wall to hang it on the nail he had just fixed, pulled the string through until it was long enough to reach the ground outside, dropped the ball after it, picked up the other nail, the hooks and the wooden shapes, and hurried out and down the steps. The other two ran down after him.
He cut off the ball of string and put it in his pocket. Then he fastened one of his hooks to the string, tying the two ends of the string together so that neither end should slip through the ring high up on the end of the barn.
“If it ever comes down,” he said, “don’t either of you try reaching out of that window to put it right again. Wait for Nancy or me.”
He hung the triangle on the hook by a hole in one of its corners. Then, hand over hand, he hoisted it up until it reached the nail on the wall, where it hung staring white against the dark weather-beaten stones.
“It’ll hang either way,” he said, “pointing up or down. There’s a hole in one of its sides on purpose. And you can make the other one hang either like a square or like a diamond. And the double hooks are so that you can hang one above another. Well, we’ll soon know if it works. Watch Holly Howe.”
“There’s someone at the window,” said Dick, whose telescope was already pointing at Mars. “Red-caps.”
“Nancy and Peggy.”
“The black square’s going!” cried Dorothea.
“They’re hauling it down,” said John. “They’ve seen all right. Yes. I thought so. There comes the triangle!”
A black triangle was climbing slowly up the white wall above the upper window at the end of the farm.
“Now we’ll try the other way.” He hauled his own white triangle down, unhooked it, and hooked it on again by a hole in the middle of one of its sides, so that it hung point downwards.
“South cone,” he said. “When they hoist that in harbour it means a storm from the south.”
“May I pull it up?” said Dick.
“Go ahead!” said John. “Your signal station.”
“Observatory,” said Dick, but he hoisted away all the same, and the triangle had no sooner reached the nail than that other triangle on the wall of Holly Howe shot downwards. A moment later it was climbing again, and this time, it too, was upside down.
“Good work!” said John. “Hullo! Theirs is going down again. They want to start skating. Anyway we’ve done enough for today. All we’ve got to do now is to make a code. Half a minute! I’ll whack another nail in down here, so that you can belay the halyards and leave a signal hoisted, without having to stand by and hang on.”
“Halyards?” said Dick.
“String,” said Dorothea.
A good place was found for a nail, within easy reach of the ground. John drove it in and showed Dick and Dorothea how to fasten their halyards. Two or three times, just for practice, they hoisted square and triangle, and both together. There were no answering signals from Holly Howe, but that, they knew, was because the others were already climbing the hillside.
John explained how the idea had come during the flashings of the night before. “You see, this way, we’ll be able to signal what the plans are for the day even before you know Morse. Nancy said last night you’d got to learn.”
“But what are the signals going to mean?” asked Dick.
“Look here,” said John, “we’ve got four single ones. North cone, with the triangle right way up; south cone, the other way; square, and diamond. And then by hanging two together, one above another, we can make a whole lot more. The main thing is to be able to say what the plans for the day are. We want to be able to hang up something meaning ‘Come to the igloo’ or ‘Come to Holly Howe.’ ”
“Or ‘Come to Mrs Dixon’s,’ ” said Dorothea.
But very little had been done towards making a code when they saw two red-capped explorers leaping through the dead bracken on the other side of the tarn.
“Here they are,” cried Dorothea.
Hurriedly the halyards were belayed, the wooden triangle and square stowed with the hooks in the loft. Hurriedly they picked up their knapsacks and ran down the steps. Already Susan, Titty, and Roger were in sight. There was a distant cheer and the sun glinted on Roger’s skates as he held them high above his head.
“You see,” John was saying as they crossed the ice together, “the whole point of these signals is that once they’re hoisted there’s no need to hang about for an answer. We can start for wherever we’re going, and you’ll know where to come. We can hoist the signals the moment Nancy comes over in the morning, and we can leave them up till we come back. No one will be able to read them except us.”
It certainly sounded as if Dorothea and Dick were considered members of the party. But it was the skating that settled it.
“Jib-booms and bobstays!” shouted