'Yes, of course.'

'On the other hand, the number of people that can be housed and sheltered in a building depends essentially on its volume. Since the ratio of surface to volume is much less for a large building than for a small one it follows that large buildings will house people at a far lower fuel consumption per head. If there is to be an endless repet.i.tion of periods of intense cold, our fuel resources will admit of no other arrangement.'

'Why do you say "if", Kingsley?' asked Parkinson.

'Because so many queer things have happened. I won't be satisfied with our predictions of what is going to happen next, until I can really understand what has happened already.'

'It might be worth while mentioning the possibility of long-term climatic changes,' remarked Marlowe. 'Although this may not be of very great importance in the next year or two, I can't see how it can fail to be vitally important in the long run a.s.suming we're going to have these bi-annual eclipses of the Sun.'

'What have you in mind, Geoff?'

'Well, surely we can't avoid moving into a new Ice Age. Past Ice Ages show how delicately the Earth's climate is balanced. Two periods of intense cold, one in winter and the other in summer, must tip the balance on the Ice Age side the Ice Age plus side, I would say.'

'You mean that ice sheets will sweep down over Europe and North America?'

'I can't see how it can be otherwise, although it won't happen in the next year or two. It'll be a slow c.u.mulative process. As Chris Kingsley says, Man'll have to come to terms with his environment. And I guess the terms won't be altogether to his liking.'

'Ocean currents,' said Alexandrov.

'I don't understand,' said the Prime Minister.

'What I imagine Alexis means,' Kingsley remarked, 'is that there is no certainty that the present pattern of ocean currents will be maintained. If it isn't, the effects might be completely disastrous. And this might happen quite quickly, quicker than an Ice Age.'

'You said it,' nodded Alexandrov. 'Gulf Stream go, gets b.l.o.o.d.y cold.'

The Prime Minister felt he had heard enough.

During November the pulse of mankind quickened. And as Governments got matters more and more in hand the desire for communication between the various pockets of humanity strengthened. Telephone lines and cables were repaired. But it was to radio that men turned in the main. Long wave radio transmitters were soon working normally, but of course they were useless for long distance communication. For this, short wave transmitters were put into operation. But the short wave transmitters failed to work, and for a reason that was soon discovered. The ionization of the atmospheric gases at a height of about fifty miles turned out to be abnormally high. This was giving rise to an excessive amount of collisional damping, as the radio engineers called it. The excessive ionization was caused by the radiation from the very hot upper reaches that were still producing the blue shimmering nights. In short, radio fade-out conditions were operative.

There was only one thing to be done: to shorten the transmitting wave-length. This was tried down to a wave-length of about one metre, but still the fade-out continued; and no suitable transmitters on still lower wave-lengths were available, since lower wave-lengths were never widely used before the coming of the Cloud. Then it was remembered that Nortonstowe possessed transmitters that would work from one metre down as far as one centimetre. Moreover the Nortonstowe transmitters were capable of handling an enormous quant.i.ty of information, as Kingsley was not slow to point out. It was accordingly decided to make Nortonstowe a world information clearing-house. Kingsley's plan had borne fruit at last.

Intricate calculations had to be performed and, as they had to be done quickly, the electronic computer was put into operation. The problem was to find the best wave-length. If the wave-length was too long the fade-out trouble would continue. If the wave-length was too short the radio waves would stream out of the atmosphere away into s.p.a.ce instead of being bent round the Earth, as they must be to travel from London to Australia, let us say. The problem was to compromise between these extremes. Eventually a wave-length of twenty-five centimetres was decided on. This was thought to be short enough to overcome the worst of the fade-out difficulty, and yet not to be so short that too much power would get squirted out into s.p.a.ce, although it was recognized that some loss must occur.

The Nortonstowe transmitters were switched on during the first week of December. Their information-carrying capacity turned out to be prodigious, as Kingsley had predicted. Less than half an hour on the first day was sufficient to clear the whole backlog of information. To begin with, only a few Governments possessed a transmitter and receiver, but the system worked so well that soon many other Governments were lashing up equipment at all speed. Partly for this reason the volume of traffic through Nortonstowe was quite small at first. Also it was difficult to appreciate initially that an hour's talk occupied a transmission time of a small fraction of a second. But as time went on, conversation and messages became longer, and more Governments joined in. So transmission at Nortonstowe rose gradually from a few minutes a day to an hour or more.

One afternoon, Leicester, who had organized the building of the transmission system, rang Kingsley and asked him to come along to the transmitting lab.

'What's the panic, Harry?' asked Kingsley.

'We've done a fade!'

'What!'

'Yes, right out. You can see it over here. A message was coming through from Brazil. Look how the signal has gone completely.'

'It's fantastic. Must be an extremely rapid burst of ionization.'

'What d'you think we ought to do?'

'Wait, I suppose. It may be a transient effect. In fact it looks rather like it.'

'If it goes on we might shorten the wave-length.'

'Yes, we might. But scarcely anybody else could. The Americans could work up a new wave-length pretty quickly, and probably the Russians as well. But it's doubtful if many of the others could. We've had enough trouble getting 'em to build their present transmitters.'

'Then there's nothing to do but hang on?'

'Well, I don't think I should try transmitting, because you'll never know if the messages get through. I should just leave the receiver on recorder. Then we shall have any stuff that happens to come through if conditions improve, that is to say.'

There was a brilliant aurora-type display that night, which the Nortonstowe scientists took to be a.s.sociated with the sudden burst of ionization high in the atmosphere. They had no idea of the cause of the ionization, however. Very large disturbances of the Earth's magnetic field were also noted.

Marlowe and Bill Barnett discussed the matter as they strolled around, admiring the display.

'My G.o.d, look at those orange-coloured sheets,' said Marlowe.

'What baffles me, Geoff, is that this is obviously a low-level display. You can tell that from the colours. I suppose we ought to have a shot at getting a spectrum, although I'd swear to it from what we can see right now. I'd say that all this is going on not more than fifty miles up, probably less. It's in just the place where we've been getting all the excessive ionization.'

'I know what you're thinking, Bill. That it's easy to imagine a sudden puff of gas. .h.i.tting the extreme outside of the atmosphere. But that would produce a disturbance much higher up. It's difficult to believe this is due to impact.'

'No, I don't think it possibly can be. It looks to me much more like an electrical discharge.'

'The magnetic disturbances would check with that.'

'But you see what this means, Geoff? This isn't from the Sun. Nothing like it from the Sun has ever happened before. If it's an electrical disturbance, it must come from the Cloud.'

Leicester and Kingsley hurried along to the communication lab after breakfast the following morning. A short message from Ireland had come in at 6.20. A long message from the U.S. had started at 7.51, but after three minutes there had been a fade and the rest of the message was lost. A short message from Sweden was received about midday, but a longer message from China was interrupted by fade-out soon after two o'clock.

Parkinson joined Leicester and Kingsley at tea.

'This is a most disturbing business,' he said.

'I can imagine so,' answered Kingsley. 'And it's another queer business.'

'Well, it's certainly annoying. I thought we'd got this communication problem in hand. In what way is it queer?'

'In that we seem to be on the verge of transmission the whole time. Sometimes messages come through and sometimes they don't, as if the ionization is oscillating up and down.'

'Barnett thinks that electrical discharges are going on, So wouldn't you expect oscillations?'

'You're becoming quite a scientist, aren't you, Parkinson?' laughed Kingsley. 'But it isn't as easy as that,' he went on. 'Oscillation yes, but hardly oscillations like the ones we've been getting. Don't you see how odd it is?'

'No, I can't say I do.'

'The messages from China and the U.S., man! We got a fade-out on each of 'em. That seems to show that when transmission is possible it's only barely possible. The oscillations seem to be making transmission just possible but only by the slightest margin. That might happen once by chance but it's very remarkable that it should happen twice.'

'Isn't there a flaw there, Chris?' Leicester chewed his pipe, and then pointed with it. 'If discharges are going on, the oscillations might be quite rapid. Both the messages from the U.S. and China were long, over three minutes. Perhaps the oscillations last about three minutes. Then you can understand why we get short messages complete, like those from Brazil and Iceland, while we never get a complete long message.'

'Ingenious, Harry, but I don't believe it. I was looking at your signal record of the U.S. message. It's quite steady, until the fade-out starts. That doesn't look like a deep oscillation, otherwise the signal would vary even before the fade-out. Then if oscillations are going on every three minutes, why aren't we getting a lot more messages, or at any rate fragments of them? I think that's a fatal objection.'

Leicester chewed his pipe again.

'It certainly looks like it. The whole thing's d.a.m.n strange.'

'What do you propose to do about it?' asked Parkinson.

'It might be a good idea, Parkinson, if you were to ask London to cable Washington asking for transmissions to be sent for five minutes every hour, starting on the hour. Then we shall know what messages are not being received, as well as those that do come through. You might also like to apprise other Governments of the situation.'

No further transmissions were received during the next three days. Whether this was due to fade-out or because no messages were sent was not known. In this unsatisfactory state of affairs a change of plan was decided on. As Marlowe told Parkinson: 'We've decided to look into this business properly, instead of depending on chance transmissions.'

'How do you intend to do that?'

'We're arranging to point all our aerials upwards, instead of more or less towards the horizon.Then we can use our own transmissions to investigate this unusual ionization. We'll pick up reflections of our own transmissions, that is to say.'

For the next two days the radio astronomers were hard at work on the aerials. It was late in the afternoon of 9 December by the time every arrangement had been made. Quite a crowd a.s.sembled in the lab to watch results.

'O.K. let her rip,' said someone.

'What wave-length shall we start on?'

'Better try one metre first,' suggested Barnett. 'If Kingsley is right in supposing that twenty-five centimetres is on the verge of transmission, and if our ideas on collision damping are correct, this ought to be about critical for vertical propagation.'

The one-metre transmitter was switched on.

'It's going through,' Barnett remarked.

'How do you know that?' Parkinson asked Marlowe.

'There's nothing but very weak return signals,' answered Marlowe. 'You can see that on the tube. Most of the power is being absorbed or is going right through the atmosphere into s.p.a.ce.'

The next half hour was spent in gazing at electrical equipment and in technical talk. Then there was a rustle of excitement.

'Signal's going up.'

'Look at it!' exclaimed Marlowe. 'It's going up with a rush!'

The return signal continued to grow for about ten minutes.

'It's saturated. We're getting total reflection now, I'd say,' said Leicester.

'Looks as though you were right, Chris. We must be quite near the critical frequency. Reflection is coming from a height of just under fifty miles, more or less where we expected it. Ionization there must be a hundred to a thousand times normal.'

A further half hour was spent in measurements.

'Better see what ten centimetres does,' remarked Marlowe.

There was a pressing of switches.

'We're on ten centimetres now. It's going right through, as of course it ought to,' announced Barnett.

'This is unbearably scientific,' said Ann Halsey. 'I'm going off to make tea. Come and help, Chris, if you can leave your meters and dials for a few minutes.'

Some time later while they were drinking tea and conversing generally, Leicester gave a startled cry.

'Heavens above! Look at this!'

'It's impossible!'

'But it's happening.'

'The ten-centimetre reflection is rising. It must mean that the ionization is going up at a colossal rate,' Marlowe explained to Parkinson.

'The d.a.m.n thing's saturating again.'

'It means the ionization has increased a hundredfold in less than an hour. It's incredible.'

'Better put the one-centimetre transmitter on, Harry,' Kingsley said to Leicester.

So the ten-centimetre transmission was changed to a one-centimetre transmission.

'Well, that's going through all right,' someone remarked.

'But not for long. In another half hour the one-centimetre will be trapped, mark my words,' said Barnett.

'Incidentally what message is being sent?' asked Parkinson.

'None,' answered Leicester, 'we're only sending C.W. continuous wave.'

'As if that explained everything,' thought Parkinson.

But although the scientists sat around for a couple of hours or more nothing further of note happened.

'Well, it's still going through. We'll see what it looks like after dinner,' said Barnett.

After dinner the one-centimetre transmission was still going through.

'It might be worth switching back to ten centimetres,' suggested Marlowe.

'O.K. let's try again.' Leicester flicked the switches. 'That's interesting,' he said. 'We're going through on ten centimetres now. The ionization seems to be dropping, and pretty rapidly too.'

'Negative ion formation probably' from Weichart.

Ten minutes later Leicester whooped with excitement.

'Look, the signal's coming in again!'

He was right. During the next few minutes the reflected signal grew rapidly to a maximum value.