The boy was tough: he gazed intently at the zenith for almost a minute, as if hoping to see the thousands of men and millions of tons of material poised there beyond the deep blue of the sky. Then he closed his eyes with a grimace, shook his head, and looked down at his feet for an instant, as if to reassure himself that he was still on the solid, dependable earth.

He reached out a cautious hand, and stroked the narrow ribbon linking the planet with its new moon.

“What would happen,” he asked, “if it broke?”

That was an old question; most people were surprised at the answer.

“Very little. At this point, it's under practically no tension. If you cut the tape it would just hang there, waving in the breeze.”

Kingsley made an expression of distaste; both knew, of course, that this was a considerable over-simplification. At the moment, each of the four tapes was stressed at about a hundred tons – but that was negligible compared to the design loads they would be handling when the system was in operation and they had been integrated into the structure of the Tower. There was no point, however, in confusing the boy with such details.

Dev thought this over; then he gave the tape an experimental flick, as if he hoped to extract a musical note from it. But the only response was an unimpressive “click” that instantly died away.

“If you hit it with a sledge-hammer,” said Morgan, “and came back about ten hours later, you'd be just in time for the echo from Midway.”

“Not any longer,” said Kingsley. “Too much damping in the system.”

“Don't be a spoil-sport, Warren. Now come and see something really interesting.”

They walked to the centre of the circular metal disc that now capped the mountain and sealed the shaft like a giant saucepan lid. Here, equidistant from the four tapes down which the Tower was being guided earthwards, was a small geodesic hut, looking even more temporary than the surface on which it had been erected. It housed an oddly-designed telescope, pointing straight upwards and apparently incapable of being aimed in any other direction.

“This is the best time for viewing, just before sunset; then the base of the Tower is nicely lit up.”

“Talking of the sun,” said Kingsley, “just look at it now. It's even clearer than yesterday.” There was something approaching awe in his voice, as he pointed at the brilliant flattened ellipse sinking down into the western haze. The horizon mists had dimmed its glare so much that one could stare at it in comfort.

Not for more than a century had such a group of Spots appeared; they stretched across almost half the golden disc, making it seem as if the sun had been stricken by some malignant disease, or pierced by falling worlds. Yet not even mighty Jupiter could have created such a wound in the solar atmosphere; the largest spot was a quarter of a million kilometres across, and could have swallowed a hundred Earths.

“There's another big auroral display predicted for tonight – Professor Sessui and his merry men certainly timed it well.”

“Let's see how they're getting on,” said Morgan, as he made some adjustments to the eye-piece. “Have a look, Dev.”

The boy peered intently for a moment, then answered: “I can see the four tapes, going inwards – I mean upwards – until they disappear.”

“Nothing in the middle?”

Another pause. “No – not a sign of the Tower.”

“Correct – it's still six hundred kilometres up, and we're on the lowest power of the telescope. Now I'm going to zoom. Fasten your seatbelt.”

Dev gave a little laugh at the ancient clichй, familiar from dozens of historical dramas. Yet at first he could see no alteration, except that the four lines pointing towards the centre of the field were becoming a little less sharp. It took him a few seconds to realise that no change could be expected as his point of view hurtled upwards along the axis of the system; the quartet of tapes would look exactly the same at any point along its length.

Then, quite suddenly, it was there, taking him by surprise even though he had been expecting it. A tiny bright spot had materialised in the exact centre of the field; it was expanding as he watched it, and now for the first time he had a real sensation of speed.

A few seconds later, he could make out a small circle – no, now both brain and eye agreed that it was a square. He was looking directly up at the base of the Tower, crawling earthwards along its guiding tapes at a couple of kilometres a day. The four tapes had now vanished, being far too small to be visible at this distance. But that square fixed magically in the sky continued to grow, though now it had become fuzzy under the extreme magnification.

“What do you see?” asked Morgan.

“A bright little square.”

“Good – that's the underside of the tower, still in full sunlight. When it's dark down here you can see it with the naked eye for another hour before it enters the earth's shadow. Now, do you see anything else?”

“Nooo…” replied the boy, after a long pause.

“You should. There's a team of scientists visiting the lowest section to set up some research equipment. They've just come down from Midway. If you look carefully you'll see their transporter – it's on the south track – that will be the right side of the picture. Look for a bright spot, about a quarter the size of the Tower.”

“Sorry, Uncle – I can't find it. You have a look.”

“Well, the seeing may have got worse. Sometimes the Tower disappears completely though the atmosphere may look -”

Even before Morgan could take Dev's place at the eyepiece, his personal receiver gave two shrill double beeps. A second later, Kingsley's alarm also erupted.

It was the first time the Tower had ever issued a four-star emergency alert.

40. The End of the Line

No wonder they called it the “Transiberian Railway”. Even on the easy downhill run, the journey from Midway Station to the base of the Tower lasted fifty hours.

One day it would take only five, but that still lay two years in the future, when the tracks were energised and their magnetic fields activated. The inspection and maintenance vehicles that now ran up and down the faces of the Tower were propelled by old-fashioned tyres, gripping the interior of the guidance slots. Even if the limited power of the batteries permitted, it was not safe to operate such a system at more than five hundred kilometres an hour.

Yet everyone had been far too busy to be bored. Professor Sessui and his three students had been observing, checking their instruments, and making sure that no time would be wasted when they transferred into the Tower. The capsule driver, his engineering assistant, and the one steward who comprised the entire cabin staff were also fully occupied, for this was no routine trip. The “Basement”, twenty-five thousand kilometres below Midway – and now only six hundred kilometres from Earth – had never been visited since it was built. Until now, there had been no purpose in going there, since the handful of monitors had never reported anything amiss. Not that there was much to go wrong, as the Basement was merely a fifteen-metre-square pressurised chamber – one of the scores of emergency refuges at intervals along the Tower.

Professor Sessui had used all his considerable influence to borrow this unique site, now crawling down through the ionosphere at two kilometres a day towards its rendezvous with Earth. It was essential, he had argued forcibly, to get his equipment installed before the peak of the current sunspot maximum.

Already, solar activity had reached unprecedented levels, and Sessui's young assistants often found it hard to concentrate on their instruments; the magnificent auroral displays outside were too much of a distraction. For hours on end, both northern and southern hemispheres were filled with slowly moving curtains and streamers of greenish light, beautiful and awe-inspiring – yet only a pale ghost of the celestial firework displays taking place around the poles. It was rare indeed for the aurora to wander so far from its normal domains; only once in generations did it invade the equatorial skies.