'We've got the results from the electronic computer,' he said. 'Good thing I insisted on having that computer. It looks as though we're all right so far as radiation is concerned. We've got a factor of about ten in hand and that should be safe enough. There's going to be an awful lot of lethal stuff coming downward from the top of the atmosphere though X-rays and ultra-violet light. But it seems as if it won't get through to the bottom of the atmosphere. We shall be pretty well shielded down at sea-level. But the situation won't be so good in the high mountains. I think people will have to be brought down. Places like Tibet will be impossible.'

'But, by and large, you think we'll be all right?'

'I just don't know. Frankly, Parkinson, I'm worried. It's not this radiation business. I think we're all right there. But I don't agree with Dave Weichart about convection, and I don't think he's as confident as he was. You remember his point about there being no convection because of the temperature increasing outwards. That's all very well under ordinary conditions. Temperature inversions, as they're called, are well known, particularly in Southern California, where Weichart comes from. And it's quite true that there's no vertical movement of the air in a temperature inversion.'

'Well then, what are you worried about?'

'The top of the atmosphere, the part that the Cloud is. .h.i.tting. There must be convection at the top, because of the impact from outside. This convection certainly won't penetrate through to the bottom of the atmosphere. Weichart's right there. But it must penetrate downwards a little way. And in the region in which it does there'll be a big transference of heat.'

'But so long as the heat doesn't get to the bottom will that matter?'

'It may do. Consider things as they'll occur day by day. The first day there'll be a little penetration of the currents. Then at night we shall lose not only the hydrogen that has come in during the day but also the part of the atmosphere down to which the currents have penetrated. So in the first day and night we shall lose an outer skin of our atmosphere, quite in addition to the hydrogen. Then the next day and night we shall lose another skin. And so on. Day by day the atmosphere will be stripped off in a series of skins.'

'Will it last for a month?'

'That's exactly the problem. And I can't tell you the answer. Maybe it won't last ten days. Maybe it'll last a whole month quite easily. I just don't know.'

'Can't you find out?'

'I can try, but it's horribly difficult to make sure that every important factor is included in the calculations. It's much worse than the radiation problem. Undoubtedly we can get some sort of answer but I don't know that I'd give it much weight. I can tell you right now that it's going to be a touch-and-go business. Frankly again, I don't believe we shall be much wiser six months from now. This is probably one of those things that are too complicated for direct calculation. We shall have to wait and see, I'm afraid.'

'What am I to tell London?'

'That's up to you. You certainly ought to tell 'em about evacuating high mountain districts even though there aren't any high enough to matter in Britain. But I leave it to your judgement how much of the rest you tell 'em.'

'Not very nice, is it?'

'No. If you find it getting you down I'd recommend a talk with one of the gardeners, Stoddard by name. He's so slow that nothing would worry him, not even the atmosphere being sprayed off.'

By the third week in January the fate of Man was to be read in the skies. The star Rigel of Orion was obscured. The sword and belt of Orion and the bright star Sirius followed in subsequent weeks. The Cloud might have blotted out almost any other constellation, except perhaps the Plough, without its effect being so widely noted.

The Press revived its interest in the Cloud. 'Progress reports' were published daily. Bus companies were finding their Night-time Mystery Tours increasingly popular. 'Listener research' showed a threefold increase in the audience for a series of B.B.C. talks on astronomy.

At the end of January perhaps one person in four had actually observed the Cloud. This was not a suffficient proportion to control public opinion, but it was sufficient to persuade the majority that it was high time that they took a look for themselves. Since it was scarcely possible for a majority of town dwellers to move at night into the country, suggestions were made for the shutting off of town lighting systems. These were at first resisted by munic.i.p.al authorities, but resistance only served to change polite suggestions into strident demands. Wolverhampton was the first town in Britain to impose a nightly black-out. Others quickly followed, and by the end of the second week in February the London authorities capitulated. Now at last the population at large was starkly aware of the Black Cloud, as it clutched like a grasping hand at Orion, the Hunter of the Heavens.

A closely similar pattern of events was repeated in the U.S., and indeed in every industrialized country. The U.S. had the additional problem of evacuating much of the western states, since a considerable area of populated territory there lies above 5,000 feet, the safe limit set in the Nortonstowe report. The U.S. Government had of course referred the matter to its own experts, but their conclusions turned out not to differ significantly from those of Nortonstowe. The U.S. also undertook to organize the evacuation of the Andean republics of South America.

The agrarian countries of Asia were strangely unmoved by the information supplied to them through the United Nations. Theirs was a 'wait and see' policy, which might really be said to have been the wisest course of all. For thousands of years the Asian peasant had been accustomed to natural disasters 'acts of G.o.d' as the lawyers of the West called them. To the oriental mind drought and flood, marauding tribes, plagues of locusts, disease, were to be suffered pa.s.sively, and so was the new thing in the sky. In any case life offered them little and consequently was not set at an unduly high price.

The evacuation of Tibet, Sinkiang, and Outer Mongolia was left to the Chinese. With cynical indifference nothing at all was done by them. The Russians, on the other hand, were punctilious and prompt in their evacuation of the Pamirs and of their other highland areas. Indeed genuine efforts were made to shift the Afghans, but Russian emissaries were driven out of Afghanistan at pistol point. India and Pakistan also spared no effort to ensure the evacuation of the part of the Himalaya south of the main watershed.

With the coming of spring in the northern hemisphere the Cloud pa.s.sed more and more from the night sky to the day sky. So, although it was spreading rapidly outside the constellation of Orion, which was now completely obscured, its presence was far less obvious to the casual observer. The British still played cricket, and dug their gardens, as indeed did the Americans.

The widespread interest in gardening was favoured by an exceptionally early summer which started in mid-May. Apprehension was widespread certainly, but it was lulled to a vague outline by week after week of wonderfully clear sunny weather. Vegetable crops were ready for eating in late May.

The Government was not nearly so pleased by the excellent weather. The reason underlying it was ominous. Since its first detection, the Cloud had by now completed about ninety per cent of the journey to the Sun. It had of course been realized that more and more radiation would be reflected by the Cloud as the Sun was approached, and that a consequent rise of temperature would take place on the Earth. Marlowe's observations suggested that there would be little or no increase in the amount of visible light, a prediction that turned out to be correct. Throughout the whole of the brilliant spring and early summer there was no noticeable increase in the brightness of the sky. What was happening was that light from the Sun was impinging on the Cloud and being re-radiated as invisible heat. Fortunately, not all the light impinging on the Cloud was re-radiated in this fashion, otherwise the Earth would have become entirely uninhabitable. And fortunately quite a large fraction of the heat never penetrated inwards through our atmosphere. It was reflected and bounced back into s.p.a.ce.

By June it became clear that the temperature of the Earth was likely to be raised everywhere by some thirty degrees Fahrenheit. It is not commonly realized how near the death temperature a large fraction of the human species lives. Under very dry atmospheric conditions a man can survive up to air temperatures of about 140 Fahrenheit. Such temperatures are in fact attained in a normal summer in low-lying regions of the Western American desert and in North Africa. But under highly humid conditions, the death temperature is only about 115 Fahrenheit. Temperatures at high humidity up to 105 Fahrenheit are attained in a normal summer down the eastern seaboard of the U.S. and sometimes in the Middle West. Curiously, temperatures at the equator do not usually run above 95 Fahrenheit, although conditions are highly humid. This oddity arises from a denser cloud cover at the equator, reflecting more of the Sun's rays back into s.p.a.ce.

It will accordingly be appreciated that the margin of safety over much of the Earth amounts to no more than 20, and in some places to very much less than this. An additional rise of 30 could be viewed therefore only with the greatest apprehension.

It may be added that death results from the inability of the body to get rid of the heat that it is constantly generating. This is necessary in order to maintain the body at its normal working temperature of about 98 Fahrenheit. An increase of body temperature to 102 produces illness, 104 produces delirium, and 106 or thereabouts produces death. It may be wondered how the body can manage to rid itself of heat when it happens to be immersed in a hotter atmosphere, say in an atmosphere at 110. The answer is by evaporation of sweat from the skin. This happens best when the humidity is low, which explains why a man can survive at higher temperatures in low humidity, and indeed why hot weather is always pleasanter when the humidity is low.

Evidently much would depend in the days to come on the behaviour of the humidity. Here there were grounds for hope. The heat rays from the Cloud would raise the temperature of the surface of the land more rapidly than the sea, and the air temperature would rise with the land while the moisture content of the air would rise more slowly with the sea. Hence the humidity would fall as the temperature rose, at any rate to begin with. It was just this initial fall of humidity that produced the unprecedented clarity of the spring and early summer in Britain.

First estimates of the heat rays from the Cloud underrated their importance. Otherwise the American Government would never have placed their scientific advisory establishment in the western desert. They were now obliged to evacuate men and equipment. This made them more dependent for information on Nortonstowe, which therefore increased in importance. But Nortonstowe had its own difficulties.

Alexandrov summed up the general opinion at a meeting of the Cloud investigation group.

'Result impossible,' he said. 'Experiment wrong.'

But John Marlborough averred that he was not wrong. To avoid an impa.s.se it was agreed that the work should be repeated by Harry Leicester, who otherwise was concerning himself with communication problems. The work was repeated and ten days later Leicester reported back to a crowded meeting.

'To go back to the early phases. When the Cloud was first discovered it was found to be moving in towards the Sun at a speed of slightly less than seventy kilometres per second. It was estimated that the speed would gradually increase as the Sun was approached, and that the average speed eventually attained would be around eighty kilometres per second. The upshot of observations reported a fortnight ago by Marlborough is that the Cloud is not behaving as we expected. Instead of speeding up as it approaches the Sun it is actually slowing down. As you know, it was decided to repeat Marlborough's observation. The best thing will be to show a few slides.'

Only one person was pleased with the slides Marlborough. His work was confirmed.

'But d.a.m.n it all,' said Weichart, 'the Cloud must speed up as it falls through the Sun's gravitational field.'

'Unless it gets rid of momentum in some way,' countered Leicester. 'Let's look at that last slide again. You see these tiny pips right away over here. They're so small that they might be a mistake, I'll grant you. But if they're real they represent motions of about five hundred kilometres per second.'

'That's very interesting,' grunted Kingsley. 'You mean the Cloud is firing off small blobs of material at very high speed, and that's what is making it slow down?'

'You could interpret the results in that way,' answered Leicester.

'At least it's an interpretation that conforms with the laws of mechanics, and which preserves sanity in some degree.'

'But why should the Cloud behave in such a darned fashion?' asked Weichart.

'Because b.a.s.t.a.r.d inside, maybe,' suggested Alexandrov.

Parkinson joined Marlowe and Kingsley that afternoon as they were walking in the grounds.

'I've been wondering whether things are going to be altered in any important way by these new discoveries,' he said.

'Difficult to say,' answered Marlowe, puffing smoke. 'Too early to say. From now on we must keep our eyes wide open.'

'Our time schedule may get changed,' remarked Kingsley. 'We reckoned that the Cloud would reach the Sun in early July, but if this slowing down goes on it'll take longer for the Cloud to move in. It may be late July or even August before things begin to happen. And I don't give much for our estimates on heating inside the Cloud either. Changes of speed are going to alter all that.'

'Do I understand that the Cloud is slowing down in rather the same way that a rocket might slow down, by firing off bits of material at high speed?' asked Parkinson.

'That's what it looks like. We were just discussing possible reasons for it.'

'What sort of thing have you in mind?'

'Well,' continued Marlowe, 'it's quite likely that there's a pretty strong magnetic field inside this Cloud. We're already getting quite big perturbations of the Earth's magnetic field. Might of course be corpuscles from the Sun, the usual sort of magnetic storm. But I've a hunch that it's the magnetic field of the Cloud that we're beginning to detect.'

'And you think this business might be bound up with magnetism?'

'It may be so. Some process caused by an interaction of the magnetic field of the Sun with that of the Cloud. It's not at all clear just what is is happening, but out of all the explanations we've been able to think of this seems the least unlikely.' happening, but out of all the explanations we've been able to think of this seems the least unlikely.'

As the three men turned a corner, a stocky man touched his cap.

'Afternoon, gentlemen.'

'Wonderful weather, Stoddard. How's the garden?'

'Yes, sir, wonderful weather. Tomatoes are ripening already. Never known it before, sir.'

When they pa.s.sed Kingsley said: 'To be frank, if it were given to me to change places with that chap for the next three months, you know I wouldn't hesitate. What a relief to have no horizon but the ripening of tomatoes!'

Throughout the rest of June and July temperatures rose steadily all over the Earth. In the British Isles the temperature climbed through the eighties, into the nineties, and moved towards the hundred mark. People grumbled, but there was no serious distress.

The death-roll in the U.S. remained quite small, thanks largely to the air-conditioning units that had been fitted during previous years and months. Temperatures rose to the lethal limit throughout the whole country and people were obliged to remain indoors for weeks on end. Occasionally air-conditioning units failed and it was then that fatalities occurred.

Conditions were utterly desperate throughout the tropics as may be judged from the fact that 7,943 species of plants and animals became totally extinct. The survival of Man himself was only possible because of the caves and cellars he was able to dig. Nothing could be done to mitigate the stifling air temperature. The number who perished during this phase is unknown. It can only be said that in all phases together more than seven hundred million persons are known to have lost their lives. And but for various fortunate circ.u.mstances still to be recounted the number would have been far greater still.

Eventually the temperature of the surface waters of the sea rose, not so fast as the air temperature it is true, but fast enough to produce a dangerous increase of humidity. It was indeed this increase that produced the distressing conditions just remarked. Millions of people between the lat.i.tudes of Cairo and the Cape of Good Hope were subjected to a choking atmosphere that grew damper and hotter inexorably from day to day. All human movement ceased. There was nothing to be done but to lie panting, as a dog pants in hot weather.

By the fourth week of July conditions in the tropics lay balanced between life and total death. Then quite suddenly rain clouds condensed over the whole globe. Within three days not a break was anywhere to be found. The Earth was as completely cloud-shrouded as normally is the planet Venus. The temperature declined a little, owing no doubt to the clouds' reflecting more of the Sun's radiation back into s.p.a.ce. But conditions could not be said to have improved. Warm rain fell everywhere, even as far north as Iceland. The insect population increased enormously, since the torrid hot atmosphere was as favourable to them as it was unfavourable to Man and the other mammals.

Plant life flourished to a fantastic degree. The deserts flowered as they had never done at any time while Man had walked the Earth. Ironically no advantage could be taken of the sudden fertility of hitherto barren soils. No crops were planted. Except in north-west Europe and the far northlands it was all Man could do to exist. No initiative could be taken. The lord of creation was beaten to his knees by his environment, the environment that for the previous fifty years he had prided himself on being able to control.

But although there was no improvement, conditions got no worse. With little or no food, but now with plenty of water, many of those exposed to the extreme heat managed to survive. The death rate had climbed to a wholly grotesque level, but it rose no further.

A discovery of some astronomical interest was made at Nortonstowe about a week before the great cloudbank spread itself over the Earth. The existence of vast drifts of dust on the Moon was confirmed in a dramatic fashion.

The rising temperature in July changed Britain's usual cool summer to a tropical heat but no worse. The gra.s.s was soon burned and the flowers died. By the standards that prevailed over most of the Earth, Britain might be considered to have been little affected, even though the daytime temperature rose to 100 and fell during the night only to about 90. Seaside resorts were crowded and caravans were to be found everywhere along the coast.

Nortonstowe was now fortunate in possessing a large air-conditioned shelter in which more and more of the party were finding it preferable to sleep at night. Otherwise life proceeded normally, except that walks in the grounds were taken at night instead of in the heat of the Sun.

One moonlit night Marlowe, Emerson, and Knut Jensen were strolling abroad when gradually the light seemed to change. Looking up, Emerson said: 'You know, Geoff, that's darned queer. I don't see any cloud.'

'Probably very high-level ice particles.'

'Not in this heat!'

'No, I suppose it can't be.'

'And there's a queer yellow look that wouldn't be ice crystals,' added Jensen.

'Well, there's only one thing to do. When in doubt take a look. Let's go along to the telescope.'

They made their way to the dome that housed the Schmidt. Marlowe directed the six-inch finder telescope on the Moon.

'My G.o.d,' he exclaimed, 'it's boiling!'

Emerson and Jensen took a look. Then Marlowe said: 'Better go up to the house and call 'em all down. This is the sight of a lifetime. I'm going to take photographs on the Schmidt itself.'

Ann Halsey accompanied the group that hurried to the telescope in response to the urgent call from Emerson and Jensen. When it came to her turn to look through the finder Ann did not know at all what to expect. True she had a general idea of the grey, scarred, sterile surface of the Moon, but she had no knowledge of its detailed topography. Nor did she understand the meaning of the excited remarks that were pa.s.sing between the astronomers. It was rather in the sense of a duty to be done that she went to the telescope. As she adjusted the focusing k.n.o.b, a wholly fantastic world jumped into view. The Moon was a lemon- yellow colour. The usual sharp details were dulled by a giant cloud that appeared to extend over and beyond the circular outline. The cloud was fed by jets that sprang out of the darker areas. Every now and then new jets would emerge from these areas, which all the time were rippling and shimmering in an astonishing fashion.

'Come on, Ann, don't hog it. We'd like a look before the night's over,' said someone. Reluctantly she yielded her place.

'What does it mean, Chris?' Ann asked Kingsley as they walked towards the shelter.

'Do you remember what we were saying the other day about the Cloud slowing down? That it's slowing down as it gets nearer the Sun instead of speeding up?'

'I remember that everybody was worried about it.'

'Well, the Cloud is slowing down by firing out blobs of gas at very high speed. We don't know why it's doing this or how, but the work that Marlborough and Leicester are doing shows pretty certainly that it is so.'

'You're not going to tell me that one of these blobs has. .h.i.t the Moon?'

'That's exactly what I think it is. Those dark areas are gigantic drifts of dust, drifts perhaps two or three miles deep. What is happening is that the impact of the high-speed gas is causing the dust to be squirted hundreds of miles upwards from the surface of the Moon.'

'Is there any chance that one of these blobs might hit us?'

'I wouldn't have thought the chance was very great. The Earth must be a very small target. But then the Moon is an even smaller target and one of 'em has just hit the Moon!'

'What would happen if ...?'

'If one hit us? I hardly like to think. We're worried enough about what's likely to happen if the Cloud hits us at a speed of perhaps fifty kilometres a second. It would be appalling if we were hit at the speed of one of those blobs, which must be the best part of a thousand kilometres a second. I suppose the whole of the Earth's atmosphere would simply be sprayed outwards into s.p.a.ce, just like the Moon's dust.'

'What I can't understand about you, Chris, is how you can know all these things and yet get so worked up about politics and politicians. It seems so unimportant and trivial.'

'Ann, my dear, if I spent my time thinking about the situation as it really is, I should be off my head in a couple of days. Some men would go off their heads. Others'd take to drink. My form of escapism is to roar at politicians. Old Parkinson knows perfectly well that it's only a sort of game we're playing. But quite seriously, from now on survival is to be measured in hours.'

She moved in closer to him.

'Or perhaps I should put it more poetically,' he murmured.

'Come kiss me, sweet and twenty Life's a stuff will not endure.'

Arrival

From the end of July a night watch was kept at the Nortonstowe shelter. Joe Stoddard was on the rota, as was natural since his work as a gardener had ceased by that time. Gardening was not an activity suited to the tropical heat.

It came about that Joe's watch fell on the night of 27 August. No dramatic action took place. Yet at 7.30 the following morning Joe knocked hesitantly on Kingsley's bedroom door. The previous evening Kingsley together with quite a number of other worthies had caroused somewhat heartily. So at first he was scarcely aware that Joe was trying to give him some message. Gradually he realized that the cheerful gardener was unusually solemn.

'It's not there, sir, it's not there.'

'What's not there? For heaven's sake go and fetch me a cup of tea. I've got a mouth like the bottom of a parrot's cage.'