The Black Cloud

Change For the Better

Although nobody realized it at the time, the occasion of the Prime Minister’s visit was very nearly the worst moment in the whole episode of the Black Cloud. The first evidence of improving conditions was discovered by the radio astronomers, appropriately so since at no time did they discontinue their observations of the Cloud, even though this meant working out of doors in most distressing conditions. On 6 October John Marlborough called a meeting. Word went round that something important was in the offing, so the meeting was well attended

Marlborough showed how his observations indicated that the amount of gas lying between the Earth and the Sun had been decreasing steadily throughout the previous ten days or so. It seemed as if the amount of gas had halved about every three days. If this behaviour continued for another fortnight the Sun would come clear altogether — but of course there was no certainty that it would continue.

Marlborough was asked if the Cloud seemed to be moving away from the Sun altogether. To this he answered that there was no such evidence. What appeared to be happening was that the material of the Cloud was distributing itself in such a fashion that the Sun would be able to shine through in our direction, but not of course in all other directions.

“Isn’t it a bit too much to hope that the Cloud will just happen to come clear in our direction?’ asked Weichart.

“It’s odd certainly,” answered Marlborough. “But I’m only giving you the evidence for what it’s worth. I’m not giving any interpretation.”

What eventually turned out to be the correct explanation was suggested by Alexandrov, although nobody took much notice at the time, probably because of the way Alexandrov chose to express himself.

“Disk stable configuration,” said he. “Probably Cloud settling into … disk.”

There were grins and someone exclaimed:

“Need we have these military adjectives, Alexis?”

Alexandrov looked surprised.

“Not military. Am scientist,” he insisted.

After this diversion the Prime Minister said:

“If I may return to more parliamentary language, do I understand from what has been said that the present crisis will be at an end in a fortnight from now?”

“If the present trend continues,” answered Marlborough.

“Then we must keep a close watch and have ourselves apprised of the situation.”

“Masterly conclusion!’ groaned Kingsley.

It is safe to say that never in the history of science had measurements been made more anxiously than those conducted during the following days by the radio astronomers. The curve on which they plotted their results became quite literally a curve of life or death. If it continued to decline it meant life; if the decline ceased and the curve started to climb it meant death.

A new point was added to the graph every few hours. All persons capable of appreciating the issues were to be found hanging around waiting for the next point, throughout the night as well as during the dusky, faint daytime. For four days and nights the curve continued to decline but on the fifth day the decline eased off, while on the sixth day there were signs of the decline changing to a rise. Scarcely anyone spoke, except for an occasional terse sentence. The tension was indescribably fierce. Then on the seventh day the decline was resumed and on the eighth day the curve was descending more steeply than ever. The intense stress was followed by violent reaction. By ordinary human standards, behaviour at Nortonstowe might have seemed somewhat promiscuous at all times and perhaps decidedly so at that time, although to those concerned, to those who experienced the anguish of the sixth day, nothing seemed at all untoward.

Thereafter the curve continued its descent and as it did so the amount of gas between the Earth and Sun dwindled more and more. On 19 October a focus of yellow light could be seen in the day sky. It was still faint, but it moved across the sky as the hours passed. Without question it was the Sun, seen for the first time since the beginning of August, still seen through a veil of gas and dust. But the veil was getting thinner and thinner. By 24 October the Sun shone again in full strength on a frozen Earth.

Those who have experienced the coming of sunrise after a cold night in the desert will have a faint idea of the joy brought by the dawn of 24 October 1965. A word about religion may be in order. During the approach of the Cloud all manner of religious beliefs had flourished mightily. During the spring, the Jehovah’s Witnesses had robbed all other speakers in Hyde Park of their audiences. Incumbents of the Church of England had been astonished to find themselves preaching to overflowing congregations. All this was swept aside on 24 October. Everyone, men and women of all creeds — Christian, Atheist, Mohammedan, Buddhist, Hindu, Jew — all became pervaded to their innermost beings with the emotional complex of the old Sun-worshippers. True, Sun-worship never became an established religion, for it had no central organization, but the undertones of the ancient religion were set vibrating and were never again damped out.

Tropical areas were the first to thaw. Ice disappeared from the rivers. Snow melted with more flooding, but the effects were marginal compared with what had gone before. The thaw in North America and in Europe was only partial, for in the ordinary way of things winter was coming on.

Vast as was the human suffering in the heavily industrialized countries, industrial populations fared far better than the less fortunate peoples, emphasizing the importance of inanimate energy and of the control of machines. It should be added that the situation in this respect might have been very different if the cold had continued to deepen, for relief came at a time when industrialization was on the verge of widespread collapse.

Somewhat paradoxically, among non-industrialized peoples, those of the tropics were hardest hit, while the genuinely nomadic Esquimaux came off best of all. In many parts of the tropics and semi-tropics as many as one person in two lost his life. Among the Esquimaux there was comparatively little loss of life, comparatively little more than in the normal way of things, that is to say. The heat had not been so great in the far north. The Esquimaux had found it highly unpleasant but no worse. Melting ice and snow interfered with their freedom of movement, thereby seriously reducing the area over which they could hunt. But the heat was not so great as to be lethal to them. Nor was the intense cold. They simply dug themselves into the snow and waited, and in this they were better off in many respects than the people of England.

Governments everywhere were in a shaky condition. Now, if ever, was the time for Communism to sweep the world. Now was the time for the United States to stamp out Communism. Now was the time for dissident groups to capture their Governments. But nothing of the sort happened. In the days immediately following 24 October everyone was too overcome with relief and too beaten down to contemplate such seemingly trivial matters. And by the middle of November the opportunity had passed. Humanity had begun to organize itself again into its respective communities.

The Prime Minister returned to London, feeling less unfavourably disposed towards Nortonstowe than might perhaps be expected. For one thing he had passed the time of the crisis far more comfortably than he would have done at Downing Street. For another he had shared the agony of suspense with the scientists at Nortonstowe and there is always a bond between those who have shared a common stress.

Before the Prime Minister left he was warned that there was no reason to suppose that the emergency was at an end. At a discussion, held in one of the laboratories attached to the shelter, it had been generally agreed that Alexandrov’s prognostication was correct. Marlborough said:

“It seems fairly certain that the Cloud is settling into a disk at a pretty high inclination to the ecliptic.”

“Disk stable configuration. Obvious,” grunted Alexandrov.

“It may be obvious to you, Alexis,” broke in Kingsley, “but there’s an awful lot about this business that’s not obvious to me. By the way, what would you put the outer radius of the disk at?”

“About three-quarters of the radius of the Earth’s orbit, about the same as the radius of the orbit of Venus,” answered Marlborough.

“This settling down into a disk must be a relative way of speaking,” Marlowe began. “I suppose you mean that the bulk of the material of the Cloud is settling into a disk. But there must be quite a lot of material spread through the whole of the Earth’s orbit. This is obvious from the stuff that’s hitting our atmosphere all the time.”

“God-awful cold in shadow of disk,” announced Alexandrov.

“Yes, thank goodness we’re clear of the disk, otherwise there’d still be no Sun,” Parkinson said.

“But remember that we shall not stay clear of the disk’ — this from Kingsley.

“What d’you mean by that?’ asked the Prime Minister.

“Simply that the Earth’s motion around the Sun will carry us into the shadow of the disk. Of course we shall come out of the shadow again.”

“Damn cold in shadow,” grunted Alexandrov.

The Prime Minister was worried, and with some justice.

“And how often, may I ask, is this appalling state of affairs likely to arise?”

“Twice a year! According to the present position of the disk, in February and August. The lengths of time for which the Sun will be eclipsed depends on how thin the disk gets. Probably the eclipse will last for somewhere between a fortnight and a month.

“The implications of this are certain to be extremely far-reaching,” sighed the Prime Minister.

“For once we agree,” remarked Kingsley. “Life on the Earth is not going to be impossible but it’ll have to be carried on in far less favourable circumstances. For one thing people will have to get used to living together in quite large numbers. We shall no longer be able to afford to live in individual houses.”

“I don’t follow.”

“Well, heat is lost from a building at its surface. Is that clear?”

“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 repetition 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 — assuming 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 cumulative 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 bloody 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 quantity 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 space 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 space, 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 associated 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 God, 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 hitting 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 damn 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 assembled 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 space.”

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 damn 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.

“Complete reflection now. What shall we do? Go back to one centimetre?”

“No, Harry,” said Kingsley. “My revolutionary suggestion is that we go upstairs to the sitting-room, where we drink coffee and where we listen to music played by Ann’s fair hand. I’d like to switch off for an hour or two and come back later.”

“What on earth is the idea, Chris?”

“Oh, just a hunch, a crazy idea, I suppose. But perhaps you’ll indulge me for once in a way.”

“For once in a way!’ chuckled Marlowe. “You’ve been indulged, Chris, from the day you were born.”

“That may be so, but it’s scarcely polite to remark on it, Geoff. Come on, Ann. You’ve been waiting to try out the Beethoven Opus 106 on us. Now’s your chance.”

It was an hour and a half or so later, with the opening chords of the great sonata still ringing in their heads, that the company made its way back to the transmitting lab.

“Try the one-metre first, just for luck,” said Kingsley.

“Bet you that one-metre is completely trapped,” Barnett said as he clicked on various switches.

“No, it’s not, by John Brown’s body,” he exclaimed a few minutes later, when the equipment had warmed up. “It’s going through. It just isn’t believable, and yet it’s as plain as a pikestaff on the tube.”

“What’s your betting, Harry, on what’s going to happen next?”

“I’m not betting, Chris. This is worse than “spot the lady”.”

“I’m betting it’s going to saturate.”

“Any reasons?”

“If it saturates I’ll have reasons, of course. If it doesn’t there won’t be any reasons.”

“Playing safe, eh?”

“Signal going up,” sang out Barnett. “Looks as though Chris is going to be right. Up it goes!”

Five minutes later the one-metre signal saturated. It was completely trapped by the ionosphere, no power getting away from the Earth.

“Now try ten centimetres,” Kingsley commanded.

For the next twenty or thirty minutes the equipment was watched keenly, all comment silenced. The earlier pattern repeated. Very little reflection was obtained at first. The reflected signal then increased rapidly in intensity.

“Well, there it is. At first the signal penetrates the ionosphere. Then after a few minutes the ionization rises and we get complete trapping. What’s it mean, Chris?’ asked Leicester.

“Let’s go back upstairs and think about it. If Ann and Yvette will be kind-hearted and make another brew of coffee, perhaps we can do something towards licking this business into shape.”

McNeil came in while coffee was being prepared. He had been attending a sick child while the experiments had been going on.

“Why the air of great solemnity? What’s been happening?”

“You’re just in time, John. We’re going to run over the facts. But we’ve promised not to start until the coffee arrives.”

The coffee came, and Kingsley began his summing up.

“For John’s benefit I’ll have to start a long way back. What happens to radio waves when they’re transmitted depends on two things, the wave-length and the ionization in the atmosphere. Suppose we choose a particular wave-length for transmission and consider what happens as the degree of ionization increases. To begin with, for low ionization the radio energy streams out of the atmosphere, with very little of it getting reflected. Then as the ionization increases there is more and more reflection until quite suddenly the reflection goes up very steeply until eventually all the radio energy is reflected, none of it getting away from the Earth. We say that the signal saturates. Is that all clear, John?”

“Up to a point. What I don’t see is how the wave-length comes into it.”

“Well, the lower the wave-length, the more ionization is needed to produce saturation.”

“So while one wave-length might be completely reflected by the atmosphere, some shorter wave-length might penetrate almost completely into outer space.”

“That’s exactly the situation. But let me go back to my particular wave-length for a moment, and to the effect of rising ionization. For convenience in talking, I’d like to call it “pattern of events A”.”

“You’d like to call it what?’ asked Parkinson.

“This is what I mean:

1. A low ionization allowing almost complete penetration.

2. A rising ionization giving a reflected signal of increased strength.

3. An ionization so high that reflection becomes complete.

“This is what I call “pattern A”.”

“And what is pattern B?’ asked Ann Halsey.

“There won’t be any pattern B.”

“Then why bother with the A?”

“Preserve me from the obtuseness of women! I can call it pattern A because I want to, can’t I?”

“Of course, dear. But why do you want to?”

“Go on, Chris. She’s only pulling your leg.”

“Well, here’s a list of what happened this afternoon and evening. Let me read it out to you as a table.”

‘It certainly looks horribly systematic when it’s all put together like that,” said Leicester.

“It does, doesn’t it?”

“I’m afraid I’m not getting this’ — Parkinson.

“Nor am I,” admitted McNeil.

Kingsley spoke slowly.

“As far as I’m aware, these events can be explained very simply on one hypothesis, but I warn you it’s an entirely preposterous hypothesis.”

“Chris, will you please stop trying to be dramatic, and tell us in simple words what this preposterous hypothesis is?”

“Very well. In one breath — that on any wave-length from a few centimetres upwards our own transmissions automatically produce a rise of ionization which continues to the saturation point.”

“It simply isn’t possible.” Leicester shook his head.

“I didn’t say it was possible,” answered Kingsley. “I said it explained the facts. And it does. It explains the whole of my table.”

“I can half see what you’re driving at,” remarked McNeil.

“Am I to suppose that the ionization falls as soon as you cease transmission?”

“Yes. When we stop transmission the ionizing agent is cut off, whatever it may be — perhaps Bill’s electrical discharges. Then the ionization falls very rapidly. You see the ionization we’re dealing with is abnormally low in the atmosphere, where the gas density is large enough to give an extremely rapid rate of formation of negative oxygen ions. So the ionization dries up very quickly as soon as it isn’t being renewed.”

“Let’s go into this in a bit more detail,” Marlowe began, speaking out of a haze of aniseed smoke. “It seems to me that this hypothetical ionizing agency must have pretty good judgement. Suppose we switch on a ten-centimetre transmission. Then according to your idea, Chris, the agency, whatever it is, drives the ionization up until the ten-centimetre waves remain trapped inside the Earth’s atmosphere. And — here’s my point — the ionization goes no higher than that. It’s all got to be very nicely adjusted. The agency has to know just how far to go and no further.”

“Which doesn’t make it seem very plausible,” said Weichart.

“And there are other difficulties. Why were we able to go on so long with the twenty-five centimetre communication? That lasted for quite a number of days, not for only half an hour. And why doesn’t the same thing happen — your pattern A as you call it — when we use a one-centimetre wave-length?”

“Bloody bad philosophy,” grunted Alexandrov. “Waste of breath. Hypothesis judged by prediction. Only sound method.”

Leicester glanced at his watch.

“It’s well over an hour since our last transmission. If Chris is right we ought to get his pattern A, if we switch on again at ten centimetres, that is to say, and possibly at one metre also. Let’s try.”

Leicester and about half a dozen others went off to the lab. Half an hour later they were back.

“Still complete reflection at one metre. Pattern A on ten centimetres,” Leicester announced.

“Which looks as if it supports Chris.”

“I’m not sure that it does,” remarked Weichart. “Why didn’t the one metre give pattern A?”

“I might make some suggestions, but in a way they’re even more fantastic, so I won’t bother with ’em just for the moment. The fact is, and I insist it is a fact, that whenever we have switched on our ten-centimetre transmitter there has always been a sharp rise of atmospheric ionization, and whenever we switched off there has been a decline of ionization. Does anyone deny that?”

“I don’t deny that what has happened so far agrees with what you say,” Weichart argued. “I agree that no denial is possible there. It’s when it comes to inferring a causal connexion between our transmissions and the fluctuations of ionization that I dig my toes in.”

“You mean, Dave, that what we found this afternoon and this evening was coincidence?’ asked Marlowe.

“That’s what I mean. I grant you that the odds against such a series of coincidences are pretty big, but Kingsley’s causal connexion seems to me an out-and-out impossibility. What I feel is that the improbable can happen but the impossible cannot.”

“Impossible is too strong,” insisted Kingsley. “And I’m sure that Weichart couldn’t really defend his use of the word. What we’re faced with is a choice between two improbabilities — I said that my hypothesis seemed improbable when I first trotted it out. Moreover I agree with what Alexis said earlier on, that the only way to test a hypothesis is by its predictions. It’s about three-quarters of an hour since Harry Leicester did his last transmission. I’m going to suggest that he goes right now and does another ten-centimetre transmission.”

Leicester groaned. “Not again!”

“I predict,” went on Kingsley, “that my pattern A will be repeated. What I’d like to know is what Weichart predicts.”

Weichart didn’t quite like the turn of the argument, and he attempted to hedge. Marlowe laughed.

“He’s pinching you, Dave! You’ve got to stand up and take it. If you’re right about it being coincidence before, you’ve got to agree that Kingsley’s present prediction is very unlikely to be right.”

“Of course it’s unlikely, but it might happen that way all the same.”

“Come off it, Dave! What do you predict? Where d’you put your money?”

And Weichart was forced to admit that he put his money on Kingsley’s prediction being wrong.

“All right. Let’s go and see,” said Leicester.

While the company were filing out, Ann Halsey said to Parkinson:

“Will you help me to make more coffee, Mr Parkinson? They’ll be wanting some when they get back.”

As they busied themselves, she went on:

“Did you ever hear such a lot of talk? I used to think that scientists were of the strong silent type, but never did I hear such a gibble-gabble. What is it that Omar Khayyám says about the doctors and saints?”

“I believe it goes something like this,” answered Parkinson:

“Myself when young did eagerly frequent

Doctor and Saint, and heard great argument

About it and about, but evermore

Came out by the same door as in I went.”

“It isn’t so much the volume of talk that surprises me,” he laughed. “We get plenty of that in politics. It’s the number of mistakes they’ve made, how often things have turned out differently to what they’ve expected.”

When the party reassembled it was obvious at a glance how things had gone. Marlowe took a cup of coffee from Parkinson.

“Thanks. Well, that’s that. Chris was right and Dave was wrong. Now I suppose we must get down to trying to decide what it means.”

“Your move, Chris,” said Leicester.

“Let’s suppose then that my hypothesis is right, that our own transmissions are producing a marked effect on the atmospheric ionization.”

Ann Halsey handed Kingsley a mug of coffee.

“I’d be a lot happier if I knew what ionization meant. Here, drink this.”

“Oh, it means that the outer parts of the atoms are stripped away from the inner parts.”

“And how does this happen?”

“It can happen in many ways, by an electrical discharge, as in a flash of lightning, or in a neon tube — the sort of strip lighting we’ve got here. The gas in these tubes is being partially ionized.”

“I suppose energy is the real difficulty? That your transmissions have far too little power to produce this rise of ionization?’ said McNeil.

“That’s right,” answered Marlowe. “It’s completely impossible that our transmissions should be the primary cause of the fluctuations in the atmosphere. My God, they’d need a fantastic amount of power.”

“Then how can Kingsley’s hypothesis be right?”

“Our transmissions are not the primary cause, as Geoff says. That’s wholly impossible. I agree with Weichart there. My hypothesis is that our transmissions are acting as a trigger, whereby some very large source of power is released.”

“And where, Chris, do you suppose this source of power is to be located?’ asked Marlowe.

“In the Cloud, of course.”

“But surely it’s quite fantastic to imagine that we can cause the Cloud to react in such a fashion, and to do it with such reproducibility? You’d have to suppose that the Cloud was equipped with a sort of feedback mechanism,” argued Leicester.

“On the basis of my hypothesis that’s certainly a correct inference.”

“But don’t you see, Kingsley, that it’s utterly mad?’ Weichart exclaimed.

Kingsley looked at his watch.

“It’s almost time to go and try again, if anyone wants to. Does anyone want to?”

“In heaven’s name, no!’said Leicester.

“Either we go or we stay. And if we stay it means that we accept Kingsley’s hypothesis. Well, boys, do we go or do we stay?’ remarked Marlowe.

“We stay,” said Barnett. “And we see how the argument goes. We’ve got as far as some sort of a feedback mechanism in the Cloud, a mechanism set to churn out an enormous amount of power as soon as it receives a trickle of radio emission from outside itself. The next step, I suppose, is to speculate on how the feedback mechanism works, and why it works as it does. Anybody got any ideas?”

Alexandrov cleared his throat. Everybody waited to catch one of his rare remarks.

“Bastard in Cloud. Said so before.”

There were wide grins and a giggle from Yvette Hedelfort. Kingsley, however, remarked quite seriously:

“I remember you did. Were you serious about it, Alexis?”

“Always serious, damn it,” said the Russian.

“Without frills, what exactly do you mean, Chris?’ someone asked.

“I mean that the Cloud contains an intelligence. Before anybody starts criticizing, let me say that I know it’s a preposterous idea and I wouldn’t suggest it for a moment if the alternative weren’t even more outrageously preposterous. Doesn’t it strike you how often we’ve been wrong about the behaviour of the Cloud?”

Parkinson and Ann Halsey exchanged an amused glance.

“All our mistakes have a certain hallmark about them. They’re just the sort of mistake that it’d be natural to make if, instead of the Cloud being inanimate, it were alive.”