The Black Cloud

Opening Scenes

It was eight o’clock along the Greenwich meridian. In England the wintry sun of 7 January 1964 was just rising. Throughout the length and breadth of the land people were shivering in ill-heated houses as they read the morning papers, ate their breakfasts, and grumbled about the weather, which, truth to tell, had been appalling of late.

The Greenwich meridian southward passes through western France over the snow-covered Pyrenees, and through the eastern corner of Spain. The line then sweeps to the west of the Balearic Islands, where wise people from the north were spending winter holidays — on a beach in Minorca a laughing party might have been seen returning from an early morning bathe. And so to North Africa and the Sahara.

The primary meridian then swings towards the equator through French Sudan, Ashanti, and the Gold Coast, where new aluminium plants were going up along the Volta River. Thence into a vast stretch of ocean, unbroken until Antarctica is reached. Expeditions from a dozen nations were rubbing elbows with each other there.

All the land to the east of this line, as far as New Zealand, was turned towards the Sun. In Australia, evening was approaching. Long shadows were cast across the cricket ground at Sydney. The last overs of the day were being bowled in a match between New South Wales and Queensland. In Java, fishermen were busying themselves in preparation for the coming night’s work.

Over much of the huge expanse of the Pacific, over America, and over the Atlantic it was night. It was three a.m. in New York. The city was blazing with light, and there was still a good deal of traffic in spite of recent snow and a cold wind from the northwest. And nowhere on the Earth at that moment was there more activity than in Los Angeles. The evening was well along there, midnight: the boulevards were crowded, cars raced along the freeways, restaurants were still pretty full.

A hundred and twenty miles to the south the astronomers on Palomar Mountain had already begun their night’s work. But although the night was clear and stars were sparkling from horizon to zenith, conditions from the point of view of the professional astronomer were poor, the ‘seeing’ was bad — there was too much wind at high levels. So nobody was sorry to down tools for the midnight snack. Earlier in the evening, when the outlook for the night already looked pretty dubious, they had agreed to meet in the dome of the 48-inch Schmidt.

Paul Rogers walked the four hundred yards or so from the 200-inch telescope to the Schmidt, only to find Bert Emerson was already at work on a bowl of soup. Andy and Jim, the night assistants, were busy at the cooking stove.

“Sorry I got started,” said Emerson, “but it looks as though tonight’s going to be a complete write-off.”

Emerson was working on a special survey of the sky, and only good observing conditions were suitable for his work.

“Bert, you’re a lucky fellow. It looks as though you’re going to get another early night.”

“I’ll keep on for another hour or so. Then if there’s no improvement I’ll turn in.”

“Soup, bread and jam, sardines, and coffee,” said Andy. “What’ll you have?”

“A bowl of soup and cup of coffee, thanks,” said Rogers.

“What’re you going to do on the 200-inch? Use the jiggle camera?”

“Yes, I can get along tonight pretty well. There’s several transfers that I want to get done.”

They were interrupted by Knut Jensen, who had walked the somewhat greater distance from the 18-inch Schmidt.

He was greeted by Emerson.

“Hello, Knut, there’s soup, bread and jam, sardines, and Andy’s coffee.”

“I think I’ll start with soup and sardines, please.”

The young Norwegian, who was a bit of a leg-puller, took a bowl of cream of tomato, and proceeded to empty half a dozen sardines into it. The others looked on in astonishment.

“Judas, the boy must be hungry,” said Jim.

Knut looked up, apparently in some surprise.

“You don’t eat sardines like this? Ah, then you don’t know the real way to eat sardines. Try it, you’ll like it.”

Then having created something of an effect, he added:

“I thought I smelled a skunk around just before I came in.”

“Should go well with that concoction you’re eating, Knut,” said Rogers.

When the laugh had died away, Jim asked:

“Did you hear about the skunk we had a fortnight ago? He de-gassed himself near the 200-inch air intake. Before anybody could stop the pump the place was full of the stuff. It sure was some hundred per cent stink. There must have been the best part of two hundred visitors inside the dome at the time.”

“Lucky we don’t charge for admission,” chuckled Emerson, “otherwise the Observatory’d be sunk in for compensation.”

“But unlucky for the clothes cleaners,” added Rogers.

On the way back to the 18-inch Schmidt, Jensen stood listening to the wind in the trees on the north side of the mountain. Similarities to his native hills set off an irrepressible wave of homesickness, longing to be with his family again, longing to be with Greta. At twenty-four, he was in the United States on a two-year studentship. He walked on, trying to kick himself out of what he felt to be a ridiculous mood. Rationally he had no cause whatsoever to be dispirited. Everyone treated him with great kindness, and he had a job ideally suited to a beginner.

Astronomy is kind in its treatment of the beginner. There are many jobs to be done, jobs that can lead to important results but which do not require great experience. Jensen’s was one of these. He was searching for novae, stars that explode with uncanny violence. Within the next year he might reasonably hope to find one or two. Since there was no telling when an outburst might occur, nor where in the sky the exploding star might be situated, the only thing to do was to keep on photographing the whole sky, night after night, month after month. Some day he would strike lucky. It was true that, should he find a nova located not too far away in the depths of space, then more experienced hands than his would take over the work. Instead of the 18-inch Schmidt, the full power of the great 200-inch would then be directed to revealing the spectacular secrets of these strange stars. But at all events he would have the honour of first discovery. And the experience he was gaining in the world’s greatest observatory would stand well in his favour when he returned home — there were good hopes of a job. Then he and Greta could get married. So what on earth was he worried about? He cursed himself for a fool to be unnerved by a wind on the mountainside.

By this time he had reached the hut where the little Schmidt was housed. Letting himself in, he first consulted his notebook to find the next section of the sky due to be photographed. Then he set the appropriate direction, south of the constellation of Orion: mid-winter was the only time of the year when this particular region could be reached. The next step was to start the exposure. All that remained was to wait until the alarm clock should signal its end. There was nothing to do except sit waiting in the dark, to let his mind wander where it listed.

Jensen worked through to dawn, following one exposure with another. Even so his work was not at an end. He had still to develop the plates that had accumulated during the night. This needed careful attention. A slip at this stage would lose much hard work, and was not to be thought of.

Normally he would have been spared this last exacting task. Normally he would have retired to the dormitory, slept for five or six hours, breakfasted at noon, and only then would he have tackled the developing job. But this was the end of his ‘run’. The moon was now rising in the evening, and this meant the end of observing for a fortnight, since the nova search could not be carried on during the half of the month when the moon was in the night sky — it was simply that the moon gave so much light that the sensitive plates he was using would have been hopelessly fogged.

So on this particular day he would be returning to the Observatory offices in Pasadena, 125 miles away. The transport to Pasadena left at half past eleven, and the developing must be done before then. Jensen decided that it would be best done immediately. Then he would have four hours’ sleep, a quick breakfast, and be ready for the trip back to town.

It worked out as he had planned, but it was a very tired young man who travelled north that day in the Observatory transport. There were three of them: the driver, Rogers, and Jensen. Emerson’s run had still another two nights to go. Jensen’s friends in wind-blown, snow-wrapped Norway would have been surprised to learn that he slept as the car sped through the miles of orange groves that flanked the road.

Jensen slept late the following morning and it wasn’t until eleven that he reached the Observatory offices. He had about a week’s work in front of him, examining the plates taken during the last fortnight. What he had to do was to compare his latest observations with the other plate that he had taken in the previous month. And this he had to do separately for each bit of the sky.

So, late on this morning of 8 January 1964, Jensen was down in the basement of the Observatory buildings setting up an instrument known as the ‘blinker’. As its name implies, the ‘blinker’ was a device that enabled him to look first at one plate, then at the other, then back to the first one again, and so on in fairly rapid succession. When this was done, any star that had changed appreciably during the time interval between the taking of the two plates stood out as an oscillating or ‘blinking’ point of light, while on the other hand the vast majority of stars that had not changed remained quite steady. In this way it was possible to pick out with comparative ease the one star in ten thousand or so that had changed. Enormous labour was therefore saved because every single star did not have to be examined separately.

Great care was needed in preparing plates for use in the ‘blinker’. They must not only be taken with the same instrument, but so far as possible must be shot under identical conditions. They must have the same exposure times and their development must be as similar as the observing astronomer can contrive. This explains why Jensen had been so careful about his exposures and development.

His difficulty now was that exploding stars are not the only sort to show changes. Although the great majority of stars do not change, there are a number of brands of oscillating stars, all of which ‘blink’ in the manner just described. Such ordinary oscillators had to be checked separately and eliminated from the search. Jensen had estimated that he would probably have to check and eliminate the best part of ten thousand ordinary oscillators before he found one nova. Mostly he would reject a ‘blinker’ after a short examination, but sometimes there were doubtful cases. Then he would have to resort to a star catalogue, and this meant measuring up the exact position of the star in question. So all in all there was quite a bit of work to do before he got through his pile of plates — work that was not a little tedious.

By 14 January he had nearly finished the whole pile. In the evening he decided to go back to the Observatory. The afternoon he had spent at the California Institute of Technology, where there had been an interesting seminar on the subject of the spiral arms of the galaxies. There had been quite a discussion after the seminar. Indeed he and his friends had argued throughout dinner about it and during the drive back to the Observatory. He reckoned he would just about get through the last batch of plates, the ones he had taken on the night of 7 January.

He finished the first of the batch. It turned out a finicking job. Once again, every one of the ‘possibilities’ resolved into an ordinary, known oscillator. He would be glad when the job was done. Better to be on the mountain at the end of a telescope than straining his eyes with this damned instrument, he thought, as he bent down to the eye-piece. He pressed the switch and the second pair flashed up in the field of view. An instant later Jensen was fumbling at the plates, pulling them out of their holders. He took them over to the light, examined them for a long time, then replaced them in the ‘blinker’ and switched on again. In a rich star field was a large, almost exactly circular, dark patch. But it was the ring of stars surrounding the patch that he found so astonishing. There they were, oscillating, blinking, all of them. Why? He could think of no satisfactory answer to the question, for he had never seen or heard of anything like this before.

Jensen found himself unable to continue with the job. He was too excited about this singular discovery. He felt he simply must talk to someone about it. The obvious man of course was Dr Marlowe, one of the senior staff members. Most astronomers specialize on one or other of the many facets of their subject. Marlowe had his specialities too, but he was above all a man of immense general knowledge. Perhaps because of this he made fewer mistakes than most people. He was ready to talk astronomy at all hours of the day and night, and he would talk with intense enthusiasm to anyone, whether a distinguished scientist like himself or a young man at the threshold of his career. It was natural therefore that Jensen should wish to tell Marlowe about his curious find.

He carefully put the two plates in question in a box, switched off the electrical equipment and the lights in the basement, and made his way to the notice board outside the library. The next step was to consult the observing list. He found to his satisfaction that Marlowe was not away either at Palomar or Mount Wilson. But, of course, he might have gone out for the evening. Jensen’s luck was in, however, for a phone call soon elicited that Marlowe was at home. When he explained that he wanted to talk to him about something queer that had turned up, Marlowe said:

“Come right over, Knut, I’ll be expecting you. No, it’s all right. I wasn’t doing anything particular.”

It says much for Jensen’s state of mind that he rang for a taxi to take him to Marlowe’s house. A student with an annual emolument of two thousand dollars does not normally travel by taxi. This was particularly so in Jensen’s case. Economy was important to him because he wished to travel around the different observatories in the United States before he returned to Norway, and he had presents to buy, too. But on this occasion the matter of money never entered his head. He rode up to Altadena, clutching his box of plates, and wondered whether in some way he’d made a fool of himself. Had he made some stupid mistake?

Marlowe was waiting.

“Come right in,” he said. “Have a drink. You take it strong in Norway, don’t you?”

Knut smiled.

“Not so strong as you take it, Dr Marlowe.”

Marlowe motioned Jensen to an easy chair by the log fire (so beloved by many who live in centrally heated houses), and after moving a large cat from a second chair, sat down himself.

“Lucky you rang, Knut. My wife’s out for the evening, and I was wondering what to do with myself.”

Then, typically, he plunged straight to the issue — diplomacy and political finesse were unknown to him.

“Well, what’ve you got there?’ he said, nodding at the yellow box that Jensen had brought.

Somewhat sheepishly, Knut took out the first of his two pictures, one taken on 9 December 1963, and handed it over without comment. He was soon gratified by the reaction.

“My God!’ exclaimed Marlowe. “Taken with the 18-inch, I expect. Yes, I see you’ve got it marked on the side of the plate.”

“Is there anything wrong, do you think?”

“Nothing so far as I can see.” Marlowe took a magnifying glass out of his pocket and scanned carefully over the plate.

“Looks perfectly all right. No plate defects.”

“Tell me why you’re so surprised, Dr Marlowe.”

“Well, isn’t this what you wanted me to look at?’

“Not by itself. It’s the comparison with a second plate that I took a month later that looks so odd.”

“But this first one is singular enough,” said Marlowe. “You’ve had it lying in your drawer for a month! Pity you didn’t show it to me right away. But of course, you weren’t to know.”

“I don’t see why you’re so surprised by this one plate, though.”

“Well, look at this dark circular patch. It’s obviously a dark cloud obscuring the light from the stars that lie beyond it. Such globules are not uncommon in the Milky Way, but usually they’re tiny things. My God, look at this! It’s huge, it must be the best part of two and a half degrees across!”

“But, Dr Marlowe, there are lots of clouds bigger than this, especially in the region of Sagittarius.”

“If you look carefully at what seem like very big clouds, you’ll find them to be built up of lots of much smaller clouds. This thing you’ve got here seems, on the other hand, to be just one single spherical cloud. What really surprises me is how I could have missed anything as big as this.”

Marlowe looked again at the markings on the plate.

“It is true that it’s in the south, and we’re not so concerned with the winter sky. Even so, I don’t see how I could have missed it when I was working on the Trapezium in Orion. That was only three or four years ago and I wouldn’t have forgotten anything like this.”

Marlowe’s failure to identify the cloud — for this is undoubtedly what it was — came as a surprise to Jensen. Marlowe knew the sky and all the strange objects to be found in it as well as he knew the streets and avenues of Pasadena.

Marlowe went over to the sideboard to renew the drinks. When he came back, Jensen said:

“It was this second plate that puzzled me.”

Marlowe had not looked at it for ten seconds before he was back to the first plate. His experienced eye needed no ‘blinker’ to see that in the first plate the cloud was surrounded by a ring of stars that were either absent or nearly absent in the second plate. He continued to gaze thoughtfully at the two plates.

“There was nothing unusual about the way you took these pictures?”

“Not so far as I know.”

“They certainly look all right, but you can never be quite sure.”

Marlowe broke off abruptly and stood up. Now, as always when he was excited or agitated, he blew out enormous clouds of aniseed-scented tobacco smoke, a South African variety. Jensen marvelled that the bowl of his pipe did not burst into flames.

“Something crazy may have happened. The best thing we can do is to get another plate shot straight away. I wonder who is on the mountain tonight.”

“You mean Mount Wilson or Palomar?”

“Mount Wilson. Palomar’s too far.”

“Well, as far as I remember, one of the visiting astronomers is using the 100-inch. I think Harvey Smith is on the 60-inch.”

“Look, it would probably be best if I went up myself. Harvey won’t mind letting me have a few moments. I won’t be able to get the whole nebulosity of course, but I can get some of the star fields at the edge. Do you know the exact co-ordinates?”

“No. I phoned as soon as I’d tried the plates in the “blink”. I didn’t stop to measure them.”

“Well, never mind, we can do that on the way. But there’s no real need to keep you out of bed, Knut. Why don’t I drop you at your apartment? I’ll leave a note for Mary saying I won’t be back until sometime tomorrow.”

Jensen was excited when Marlowe dropped him at his lodging. Before he turned in that night he wrote letters home, one to his parents telling them very briefly of the unusual discovery, and another to Greta saying that he believed he’d stumbled on something important.

Marlowe drove to the Observatory offices. His first step was to get Mount Wilson on the phone and to talk to Harvey Smith. When he heard Smith’s soft southern accent, he said:

“This is Geoff Marlowe. Look, Harvey, something pretty queer has turned up, so queer that I’m wondering if you’d let me have the 60-inch for tonight. What is it? I don’t know what it is. That’s just what I want to find out. It’s to do with young Jensen’s work. Come down here at ten o’clock tomorrow and I’ll be able to tell you more about it. If you’re bored I’ll stand you a bottle of Scotch. That’s good enough for you? Fine! Tell the night assistant that I’ll be up at about one o’clock, will you?”

Marlowe next put through a call to Bill Barnett of Caltech.

“Bill, this is Geoff Marlowe ringing from the offices. I wanted to tell you that there’ll be a pretty important meeting here tomorrow morning at ten o’clock. I’d like you to come along and bring a few theoreticians along. They don’t need to be astronomers. Bring several bright boys … No, I can’t explain now. I’ll know more tomorrow. I’m going on the 60-inch tonight. But I’ll tell you what, if you think by lunch-time tomorrow that I’ve got you out on a wild-goose chase, I’ll stand you a crate of Scotch … Fine!”

He hummed with excitement as he hurried down to the basement where Jensen had been working earlier in the evening. He spent some three-quarters of an hour measuring Jensen’s plates. When at last he was satisfied that he would know exactly where to point the telescope, he went out, climbed into his car, and drove off towards Mount Wilson.

Dr Herrick, the Director of the Observatory, was astonished to find Marlowe waiting for him when he reached his office at seven-thirty the following morning. It was the Director’s habit to start his day some two hours before the main body of his staff, “in order to get some work done’, as he used to say. At the other extreme, Marlowe usually did not put in an appearance until ten-thirty, and sometimes later still. This day, however, Marlowe was sitting at his desk, carefully examining a pile of about a dozen positive prints. Herrick’s surprise was not lessened when he heard what Marlowe had to say. The two men spent the next hour and a half in earnest conversation. At about nine o’clock they slipped out for a quick breakfast, and returned in time to make preparations for a meeting to be held in the library at ten o’clock.

When Bill Barnett’s party of five arrived they found some dozen members of the Observatory already assembled, including Jensen, Rogers, Emerson, and Harvey Smith. A blackboard had been fitted up and a screen and lantern for showing slides. The only member of Barnett’s party who had to be introduced round was Dave Weichart. Marlowe, who had heard a number of reports of the abilities of this brilliant twenty-seven-year-old physicist, noted that Barnett had evidently done his best to bring a bright boy along.

“The best thing I can do,” began Marlowe, “is to explain things in a chronological way, starting with the plates that Knut Jensen brought to my house last night. When I’ve shown them you’ll see why this emergency meeting was called.”

Emerson, who was working the lantern, put in a slide that Marlowe had made up from Jensen’s first plate, the one taken on the night of 9 December 1963.

“The centre of the dark blob,” went on Marlowe, “is in Right Ascension 5 hours 49 minutes, Declination minus 30 degrees 16 minutes, as near as I can judge.”

“A fine example of a Bok globule,” said Barnett.

“How big is it?”

“About two and a half degrees across.”

There were gasps from several of the astronomers.

“Geoff, you can keep your bottle of whisky,” said Harvey Smith.

“And my crate, too,” added Bill Barnett amidst the general laughter.

“I reckon you’ll be needing the whisky when you see the next plate. Bert, keep rocking the two backwards and forwards, so that we can get some idea of a comparison,” went on Marlowe.

“It’s fantastic,” burst out Rogers, “it looks as if there’s a whole ring of oscillating stars surrounding the cloud. But how could that be?”

“It can’t,” answered Marlowe. “That’s what I saw straight away. Even if we admit the unlikely hypothesis that this cloud is surrounded by a halo of variable stars, it is surely quite inconceivable that they’d all oscillate in phase with each other, all up together as in the first slide, and all down together as in the second.”

“No, that’s preposterous,” broke in Barnett. “If we’re to take it that there’s been no slip-up in the photography, then surely there’s only one possible explanation. The cloud is moving towards us. In the second slide it’s nearer to us, and therefore it’s obscuring more of the distant stars. At what interval apart were the two plates taken?”

“Rather less than a month.”

“Then there must be something wrong with the photography.”

“That’s exactly the way I reasoned last night. But as I couldn’t see anything wrong with the plates, the obvious thing was to take some new pictures. If a month made all that difference between Jensen’s first plate and his second, then the effect should have been easily detectable in a week — Jensen’s last plate was taken on 7 January. Yesterday was 14 January. So I rushed up to Mount Wilson, bullied Harvey off the 60-inch, and spent the night photographing the edges of the cloud. I’ve got a whole collection of new slides here. They’re not of course on the same scale as Jensen’s plates, but you’Il be able to see pretty well what’s happening. Put them through one by one, Bert, and keep referring back to Jensen’s plate of 7 January.”

There was almost dead silence for the next quarter of an hour, as the star fields on the edge of the cloud were carefully compared by the assembled astronomers. At the end Barnett said:

“I give up. As far as I’m concerned there isn’t a shadow of a doubt but that this cloud is travelling towards us.”

And it was clear that he had expressed the conviction of the meeting. The stars at the edge of the cloud were being steadily blacked out as it advanced towards the solar system.

“Actually there’s no doubt at all about it,” went on Marlowe. “When I discussed things with Dr Herrick earlier this morning he pointed out that we have a photograph taken twenty years ago of this part of the sky.”

Herrick produced the photograph.

“We haven’t had time to make up a slide,” said he, “so you will have to hand it round. You can see the black cloud, but it’s small on this picture, no more than a tiny globule. I’ve marked it with an arrow.”

He handed the picture to Emerson who, after passing it to Harvey Smith, said:

“It’s certainly grown enormously over the twenty years. I’m a bit apprehensive about what’s going to happen in the next twenty. It seems as if it might cover the whole constellation of Orion. Pretty soon astronomers will be out of business.”

It was then that Dave Weichart spoke up for the first time.

“I’ve two questions that I’d like to ask. The first is about the position of the cloud. As I understand what you’ve said, the cloud is growing in its apparent size because it’s getting nearer to us. That’s clear enough. But what I’d like to know is whether the centre of the cloud is staying in the same position, or does it seem to be moving against the background of the stars?”

“A very good question. The centre seems, over the last twenty years, to have moved very little relative to the star field,” answered Herrick.

“Then that means the cloud is coming dead at the solar system.”

Weichart was used to thinking more quickly than other people, so when he saw hesitation to accept his conclusion, he went to the blackboard.

“I can make it clear with a picture. Here’s the Earth. Let’s suppose first that the cloud is moving dead towards us, like this, from A to B.

Then at B the cloud will look bigger but its centre will be in the same direction. This is the case that apparently corresponds pretty well to the observed situation.”

There was a general murmur of assent, so Weichart went on:

“Now let’s suppose that the cloud is moving sideways, as well as towards us and let’s suppose that the motion sideways is about as fast as the motion towards us. Then the cloud will move about like this. Now if you consider the motion from A to B you’ll see that there are two effects — the cloud will seem bigger at B than it was at A, exactly as in the previous case, but now the centre will have moved. And it will move through the angle AEB which must be something of the order of thirty degrees.”

“I don’t think the centre has moved through an angle of more than a quarter of a degree,” remarked Marlowe.

“Then the sideways motion can’t be more than about one per cent of the motion towards us. It looks as though the cloud is heading towards the solar system like a bullet at a target.”

“You mean, Dave, that there’s no chance of the cloud missing the solar system, of it being a near-miss, let us say?”

“On the facts as they’ve been given to us that cloud is going to score a bull’s eye, plumb in the middle of the target. Remember that it’s already two and a half degrees in diameter. The transverse velocity would have to be as much as ten per cent or so of the radial velocity if it were to miss us. And that would imply a far greater angular motion of the centre than Dr Marlowe says has taken place. The other question I’d like to ask is, why wasn’t the cloud detected sooner? I don’t want to be rude about it, but it seems very surprising that it wasn’t picked up quite a while ago, say ten years ago.”

“That of course was the first thing that sprang to my mind,” answered Marlowe. “It seemed so astonishing that I could scarcely credit the validity of Jensen’s work. But then I saw a number of reasons. If a bright nova or a supernova were to flash out in the sky it would immediately be detected by thousands of ordinary people, let alone by astronomers. But this is not something bright, it’s something dark, and that’s not so easy to pick up — a dark patch is pretty well camouflaged against the sky. Of course if one of the stars that has been hidden by the cloud had happened to be a bright fellow it would have been spotted. The disappearance of a bright star is not so easy to detect as the appearance of a new bright star, but it would nevertheless have been noticed by thousands of professional and amateur astronomers. It happened, however, that all the stars near the cloud are telescopic, none brighter than eighth magnitude. That’s the first mischance. Then you must know that in order to get good seeing conditions we prefer to work on objects near the zenith, whereas this cloud lies rather low in our sky. So we would naturally tend to avoid that part of the sky unless it happened to contain some particularly interesting material, which by a second mischance (if we exclude the case of the cloud) it does not. It is true that to observatories in the southern hemisphere the cloud would be high in the sky, but observatories in the southern hemisphere are hard put to it with their small staffs to get through a host of important problems connected with the Magellanic Clouds and the nucleus of the Galaxy. The cloud had to be detected sooner or later. It turned out to be later, but it might have been sooner. That’s all I can say.”

“It’s too late to worry about that now,” said the Director. “Our next step must be to measure the speed with which the cloud is moving towards us. Marlowe and I have had a long talk about it, and we think it should be possible. Stars on the fringe of the cloud are partially obscured, as the plates taken by Marlowe last night show. Their spectrum should show absorption lines due to the cloud, and the Doppler shift will give us the speed.”

“Then it should be possible to calculate how long the cloud will be before it reaches us,” joined in Barnett. “I must say I don’t like the look of things. The way the cloud has increased its angular diameter during the last twenty years makes it look as if it’ll be on top of us within fifty or sixty years. How long do you think it’ll take to get a Doppler shift?”

“Perhaps about a week. It shouldn’t be a difficult job.”

“Sorry I don’t understand all this,” broke in Weichart. “I don’t see why you need the speed of the cloud. You can calculate straight away how long the cloud is going to take to reach us. Here, let me do it. My guess is that the answer will turn out at much less than fifty years.”

For the second time Weichart left his seat, went to the blackboard, and cleaned off his previous drawings.

“Could we have Jensen’s two slides again please?”

When Emerson had flashed them up, first one and then the other, Weichart asked: ‘Could you estimate how much larger the cloud is in the second slide?”

“I would say about five per cent larger. It may be a little more or a little less, but certainly not very far away from that,” answered Marlowe.

“Right,” Weichart continued, “let’s begin by defining a few symbols.”

Then followed a somewhat lengthy calculation at the end of which Weichart announced:

“And so you see that the black cloud will be here by August 1965, or possibly sooner if some of the present estimates have to be corrected.”

Then he stood back from the blackboard, checking through his mathematical argument.

“It certainly looks all right — very straightforward in fact,” said Marlowe, putting out great volumes of smoke.[1]

“Yes, it seems unimpeachably correct,” answered Weichart.

At the end of Weichart’s astonishing calculation, the Director had thought it wise to caution the whole meeting to secrecy. Whether they were right or wrong, no good could come of talking outside the Observatory, not even at home. Once the spark was struck the story would spread like wildfire, and would be in the papers in next to no time. The Director had never had any cause to think highly of newspaper reporters, particularly of their scientific accuracy.

From midday to two o’clock he sat alone in his office, wrestling with the most difficult situation he had ever experienced. It was utterly antipathetic to his nature to announce any result or to take steps on the basis of a result until it had been repeatedly checked and cross-checked. Yet would it be right for him to maintain silence for a fortnight or more? It would be two or three weeks at least before every facet of the matter were fully investigated. Could he afford the time? For perhaps the tenth time he worked through Weichart’s argument. He could see no flaw in it.

At length he called in his secretary.

“Please will you ask Caltech to fix me a seat on the night plane to Washington, the one that leaves about nine o’clock? Then get Dr Ferguson on the phone.”

James Ferguson was a big noise in the National Science Foundation, controlling all the activities of the Foundation in physics, astronomy, and mathematics. He had been much surprised at Herrick’s phone call of the previous day. It was quite unlike Herrick to fix appointments at one day’s notice.

“I can’t imagine what can have bitten Herrick,” he told his wife at breakfast, “to come chasing over to Washington like this. He was quite insistent about it. Sounded agitated, so I said I’d pick him up at the airport.”

“Well, an occasional mystery is good for the system,” said his wife. “You’ll know soon enough.”

On the way from the airport to the city, Herrick would commit himself to nothing but conventional trivialities. It was not until he was in Ferguson’s office that he came to the issue.

“There’s no danger of us being overheard, I suppose?”

“Goodness, man, is it as serious as that? Wait a minute.”

Ferguson lifted the phone.

“Amy, will you please see that I’m not interrupted — no, no phone calls — well, perhaps for an hour, perhaps two, I don’t know.”

Quietly and logically Herrick then explained the situation. When Ferguson had spent some time looking at the photographs, Herrick said:

“You see the predicament. If we announce the business and we turn out to be wrong, then we shall look awful fools. If we spend a month testing all the details and it turns out that we are right, then we should be blamed for procrastination and delay.”

“You certainly would, like an old hen sitting on a bad egg.”

“Well, James, I thought you have had a great deal of experience in dealing with people. I felt you were someone I could turn to for advice. What do you suggest I should do?”

Ferguson was silent for a little while. Then he said:

“I can see that this may turn out to be a grave matter. And I don’t like taking grave decisions any more than you do, Dick, certainly not on the spur of the moment. What I suggest is this. Go back to your hotel and sleep through the afternoon — I don’t expect you had much sleep last night. We can meet again for an early dinner, and by then I’ll have had an opportunity to think things over. I’ll try to reach some conclusion.”

Ferguson was as good as his word. When he and Herrick had started their evening meal, in a quiet restaurant of his choice, Ferguson began:

“I think I’ve got things sorted out fairly well. It doesn’t seem to me to make sense wasting another month in making sure of your position. The case seems to be very sound as it is, and you can never be quite certain — it would be a matter of converting a ninety-nine per cent certainty into a ninety-nine point nine per cent certainty. And that isn’t worth the loss of time. On the other hand you are ill-prepared to go to the White House just at the moment. According to your own account you and your men have spent less than a day on the job so far. Surely there are a good many other things you might get ideas about. More exactly, how long is it going to take the cloud to get here? What will its effects be when it does get here? That sort of question.

“My advice is to go straight back to Pasadena, get your team together, and aim to write a report within a week, setting out the situation as you see it. Get all your men to sign it — so that there’s no question of the tale getting around of a mad Director. And then come back to Washington.

“In the meantime I’ll get things moving at this end. It isn’t a bit of good in a case like this starting at the bottom by whispering into the ear of some Congressman. The only thing to do is to go straight to the President. I’ll try to smooth your path there.”