“Perfect agreement,” exclaimed Marlowe. “And what’s more, the position they give is almost dead on our position. It all fits together.”
“This makes my report a much more difficult matter,” Herrick said with a frown. “It really should be written in consultation with the Astronomer Royal. I think we ought to get both him and Kingsley over here as soon as possible.”
“Absolutely right,” agreed Marlowe. “Get the Secretary on to it right away. It should be possible to get ’em over in about thirty-six hours, the morning after tomorrow. Better still, let your friends in Washington make the arrangements. And about the report, wouldn’t it be a good idea to write it in three parts? Part one could deal with our discoveries here at the Observatory. Part two would be contributed by Kingsley and the Astronomer Royal. And part three would be an account of our conclusions, especially the conclusions we reach when the British get here.”
“There’s a great deal in what you say, Geoff. I can get part one finished by the time our friends arrive. We can leave part two to them, and lastly we can thrash out our conclusions.”
“Excellent. I reckon you’ll probably get through by tomorrow. How about bringing Alison over for dinner tomorrow night?”
“I’d be glad to, delighted to, if I can get through by tomorrow afternoon. Can I leave it until then?”
“Sure, that’s fine. Just let me know tomorrow,” said Marlowe getting up.
As Marlowe was leaving, Herrick said:
“It’s pretty serious, isn’t it?”
“It certainly is. I had a sort of premonition when I first saw Knut Jensen’s pictures. I didn’t realize how bad it was until this cable arrived. The density works out in the region of 10–9 to 10–10gm. per cm3. That means it’ll block out the Sun’s light entirely.”
Kingsley and the Astronomer Royal arrived in Los Angeles early on the morning of 20 January. Marlowe was waiting to meet them at the airport. After a quick breakfast in a drug store they hit the freeway system to Pasadena.
“Goodness me, what a difference from Cambridge,” grunted Kingsley. “Sixty miles an hour instead of fifteen, blue skies instead of endless rain and drizzle, temperature in the sixties even as early in the day as this.”
He was very weary after the long flight, first across the Atlantic, then a few hours’ waiting in New York — too short to be able to do anything interesting, yet long enough to be tiresome, the epitome of air travel, and lastly the trip across the U.S.A. during the night. Still it was a great deal better than a year at sea getting round the Horn, which is what men had to do a century ago. He would have liked a long sleep, but if the Astronomer Royal was willing to go straight to the Observatory, he supposed he ought to go along too.
After Kingsley and the Astronomer Royal had been introduced to those members of the Observatory that they had not previously met, and after greetings with old friends, the meeting started in the library. With the addition of the British visitors it was the same company that had met to discuss Jensen’s discovery the previous week.
Marlowe gave a succinct account of this discovery, of his own observations, and of Weichart’s argument and startling conclusion.
“And so you see,” he concluded, “why we were so interested to receive your cablegram.”
“We do indeed,” answered the Astronomer Royal. “These photographs are most remarkable. You give the position of the centre of the cloud as Right Ascension 5 hours 49 minutes, Declination minus 30 degrees 16 minutes. That seems to be in excellent agreement with Kingsley’s calculations.”
“Now would you two care to give us a short account of your investigations?’ said Herrick. “Perhaps the Astronomer Royal could tell us about the observational side and then Dr Kingsley could say a little about his calculations.”
The Astronomer Royal gave a description of the displacements that had been discovered in the positions of the planets, particularly of the outer planets. He discussed how the observations had been carefully checked to make sure that they contained no errors. He did not fail to give credit to the work of Mr George Green.
“Heavens, he’s at it again,” thought Kingsley.
The rest of the company heard the Astronomer Royal out with interest, however.
“And so,” he concluded, “I’ll hand over to Dr Kingsley, and let him outline the basis of his calculations.”
“There is not a great deal to be said,” began Kingsley. “Granting the accuracy of the observations that the Astronomer Royal has just told us about — and I must admit to having been somewhat reluctant at first to concede this — it was clear that the planets were being disturbed by the gravitational influence of some body, or material, intruding into the solar system. The problem was to use the observed disturbances to calculate the position, mass, and velocity of the intruding material.”
“Did you work on the basis that the material acted as a point mass?’ asked Weichart.
“Yes, that seemed to be the best thing to do, at any rate to begin with. The Astronomer Royal did mention the possibility of an extended cloud. But I must confess that psychologically I’ve been thinking in terms of a condensed body of comparatively small size. I’ve only just begun to assimilate the cloud idea, now that I’ve seen these photographs.”
“How far do you think your wrong assumption affected the calculations?’ Kingsley was asked.
“Hardly at all. So far as producing planetary disturbances is concerned, the difference between your cloud and a much more condensed body would be quite small. Perhaps the slight differences between my results and your observations arise from this cause.”
“Yes, that’s quite clear,” broke in Marlowe amid aniseed smoke. “How much information did you need to get your results? Did you use the disturbances of all the planets?”
“One planet was enough. I used the observations of Saturn to make the calculations about the Cloud — if I may call it that. Then having determined the position, mass, etc., of the Cloud, I inverted the calculation for the other planets and so worked out what the disturbances of Jupiter, Mars, Uranus, and Neptune ought to be.”
“Then you could compare your results with the observations?”
“Exactly so. The comparison is given in these tables that I’ve got here. I’ll hand them round. You can see that the agreement is pretty good. That’s why we felt reasonably confident about our deductions, and why we felt justified in sending our cable.”
“Now I’d like just to know how your estimates compare with mine,” asked Weichart. “It seemed to me that the Cloud would take about eighteen months to reach the Earth. What answer do you get?”
“I’ve already checked that, Dave,” remarked Marlowe. “It agrees very well. Dr Kingsley’s values give about seventeen months.”
“Perhaps a little less than that,” observed Kingsley. “You get seventeen months if you don’t allow for the acceleration of the Cloud as it approaches the Sun. It’s moving at about seventy kilometres per second at the moment, but by the time it reaches the Earth it’ll have speeded to about eighty. The time required for the Cloud to reach the Earth works out at nearly sixteen months.”
Herrick quietly took charge of the discussion.
“Well, now that we understand each other’s point of view, what conclusions can we reach? It seems to me that we have both been under some misapprehension. For our part we thought of a much larger cloud lying considerably outside the solar system, while, as Dr Kingsley says, he thought of a condensed body within the solar system. The truth lies somewhere between these views. We have to do with a rather small cloud that is already within the solar system. What can we say about it?”
“Quite a bit,” answered Marlowe. “Our measurement of the angular diameter of the Cloud as about two and a half degrees, combined with Dr Kingsley’s distance of about 21 astronomical units, shows that the Cloud has a diameter about equal to the distance from the Sun to the Earth.”
“Yes, and with this size we can immediately get an estimate of the density of the material in the Cloud,” went on Kingsley. “It looks to me as though the volume of the cloud is roughly 1040 c.c. Its mass is about 1·3 ? 1030 gm., which gives a density of 1·3 ? 10–10 gm. per cm3.”
A silence fell on the little company. It was broken by Emerson.
“That’s an awful high density. If the gas comes between us and the Sun it’ll block out the Sun’s light completely. It looks to me as if it’s going to get almighty cold here on Earth!”
“That doesn’t necessarily follow,” broke in Barnett. “The gas itself may get hot, and heat may flow through it.”
“That depends on how much energy is required to heat the Cloud,” remarked Weichart.
