Cosmic Clearance

(See front cover)

At 10 a. m. on Jan. 1 the high-banked seats of a lecture amphitheatre at Washington University were jammed with a capacity crowd of 300--mostly scholars, a few newshawks, a handful of laymen. In the doorways and the hall outside a hundred more strained their ears. This was but one of a thousand discourses made last week at the midwinter talk carnival of the American Association for the Advancement of Science in St. Louis. But for most of the audience it marked the end of the "mystery" of cosmic rays, wrote finis to one of the most reverberating scientific controversies of the century. The tall, rugged man with deep-set eyes and heavy chin who was reading a paper was Arthur Holly Compton. Newshawks esteem this topflight physicist and Nobel Prizewinner of the University of Chicago for his ability to get things said without benefit of polysyllables. His address last week was understandable to anyone who knew what photons and ions are. He introduced one hybrid term of his own devising: isocosms, or lines of equal cosmic ray intensity on the world map. He showed on a chart how isocosms closely follow the lines of equal geomagnetic intensity. He left a definite impression that isocosms were not to be argued with.

First Finder. Like a good scientist Dr. Compton thought it best to begin at the beginning: "In order to place the results of the recent studies of cosmic rays in appropriate perspective, let us recall very briefly their early history. It is well known how at the beginning of the present century. . . ." At the beginning of the present century Geitel of Germany, experimenting with a quartz-fibre electroscope, noticed that for no apparent reason the air in his instrument gradually became more electrified or ionized. Later experimenters discovered that thick screens of lead or water shut out some of the mysterious ionizing agent, but not all. Lord Rutherford thought it might be something in the atmosphere near the ground. Goeckel of Switzerland, Hess of Vienna and Kolhorster of Potsdam made balloon flights up to five miles, found the radiation seven times stronger than at the earth's surface. Thus the rays were seen to be coming in from the cosmos beyond Earth's blanket of air. Calculation revealed them as more penetrating than the gamma rays which emerge from radium at 3,000,000 electron-volts. Stopped by the War, the cosmic ray hunt started with fresh impetus after Peace. In the U. S., brilliant, imaginative Robert Andrews Millikan of California Institute of Technology, who had won the Nobel Prize for isolating and measuring the electron, sank his recorders under 280 ft. of water in California. Some rays, after fighting their way through the atmosphere, had enough drive left to reach that depth in the lake, indicating power to thrust through 25 ft. of solid lead, which was 50 times more penetration than any other known radiation.

Millikan's Photons. It seemed natural to Dr. Millikan that the cosmic rays were light rays or photons of enormously high frequency and short wave length. He concluded that they were the by-products of atom-building in interstellar space; that when light-weight atoms suddenly combined to form heavier ones, a slight excess of matter--like bricklayer's mortar scraped from the wall--was turned into high-frequency light according to the Einstein equation. To him this was a peculiarly satisfying interpretation as it bespoke "the Creator still on the job."

Nevertheless photons are electrically neutral, are not swerved by magnetic fields. If the cosmic rays were Millikan photons, they should not tend to cluster about Earth's strongly magnetic poles, to avoid the weakly magnetic Equator. Yet a Dutchman named Clay, traveling from Holland to Java, found a drop in cosmic ray intensity at the Equator. Kolhorster took this to mean that at least some of the rays were not photons of light, but electrically charged particles of matter.

At this point Arthur Holly Compton, already a crowned king of terrestrial radiation, leaped into the cosmic quest. He had an impatient desire to collect a mass of far-flung recordings with the greatest possible speed. Eight cooperating expeditions were to measure the rays in Greenland, Denmark, India, Ceylon, Java, Tibet, South Africa, Eritrea, Spitsbergen, Switzerland. One man was to make records from Peru around the Cape of Good Hope to the U. S. Two Compton men were killed trying to scale Mt. McKinley in Alaska. Dr. Compton himself, with his wife and elder son, set out on a cosmic search that took him to a volcano brim in Hawaii, Mt. Cook in New Zealand, Panama, Peru, covered 50,000 miles. He made an airplane flight within 350 miles of the North Magnetic Pole. When all the data was in his hands, he found overwhelming evidence for variation by latitude, ranging up to 20%, concluded that most of the rays were electric corpuscles affected by the varying magnetic pulls of Earth. Dr. Millikan clung to his photons, alleging that the corpuscles were secondary rays knocked out of air atoms by the primary photons.

Retreat. At this stage the problem reached the midwinter convention of the A. A. A. S. at Atlantic City in 1932, which both Nobel Laureates attended. For a time the two seemed on the verge of noisy dispute (TIME, Jan. 9, 1933). Dr. Compton had found charged particles with energies of 30,000,000,000 volts, which could hardly be secondary rays dislodged from the air. Dr. Millikan said that anyone recording voltages over a billion must have muffed the technique.

After that dramatic standoff, Dr. Millikan has steadily, almost imperceptibly, retreated from his position, while Dr. Compton has maintained and strengthened his. Millikan's billion-volt maximum announced at Atlantic City cracked when he recognized rays at the Equator of 10,000,000,000 volts. This in turn involved yielding a point to Sir James Jeans, who had held that cosmic rays were not "birth cries" but "death cries'' of matter annihilated in the wasting stars. Ten billion volts, honest Dr. Millikan conceded, could only come from the complete annihilation of atoms. Dr. Thomas H. Johnson of the Bartol Research Foundation and others found that more cosmic rays were slanting to the east than to the west. Theorists had already shown that a positively charged corpuscle would have an eastward slant impressed on it by the Earth's magnetic field. One important Millikan defense had been that the particles observed were terrestrial secondary rays knocked out of the air by primary cosmic photons. If this were true, the latitude variation showing corpuscles should decrease toward the thin top of the atmosphere where targets were fewer. It was found, on the contrary, that in the upper air the latitude effect increased from 20% to 97 1/2%. Last autumn Dr. Millikan, addressing the National Academy of Sciences, presented recordings from nine ships showing that cosmic rays are stronger in the Eastern hemisphere than in the Western. This longitude effect could only have reference to charged particles, since the geomagnetic field is stronger in India than in the U. S. Photons were left out of the picture. Much of this history was traced by Dr. Compton last week. But with data from a dozen scientific satrapies covering 100 localities, including Antarctica, he was ready with specific answers to specific questions. What are cosmic rays? Since the latitude effect showing electric particles increases from about 20% at sea level to some 97% near the top of the atmosphere, it stands to reason that primary cosmic radiation 400 or 500 miles out in space must consist of at least 99% particles. The remaining 1% may be particles or photons or both. By checking theoretical absorption rates against those actually observed three prominent ingredients have been found in the cosmic ray. One consists of nearly equal parts of positive and negative electrons. Another, which does not penetrate far below the top of the atmosphere, is alpha particles, or positively charged nuclei of helium. The third, which reaches sea-level easily, is protons, or positively charged nuclei of hydrogen. How power fid are they? The most powerful rays can penetrate 3,200 ft. of water or 292 ft. of solid lead. For a vertical primary ray to reach the Equator requires 20,000,000,000 volts. Showers of particles knocked out of atomic nuclei by cosmic rays indicate occasional energies of 600 billion volts. Where do they come from? Directional measurements show no evidence that cosmic rays come from the sun, or the neighboring stars, or even from the great mass of stars in the Milky Way. Years ago Dr. Millikan therefore guessed that they came from the vast reaches beyond the Milky Way. The whole Milky Way is slowly rotating, carrying Earth along in the direction of Vega at some 200 mi. per sec. Therefore if the cosmic rays come from outside the great Milky Way wheel, whatever side of Earth happens to be facing Vega should receive a few more rays than the back of the planet, just as a child riding a carousel in the rain should be struck by more drops in front than in back. This small daily variation in the cosmic rays has actually been observed, so Dr. Compton agrees they must come from the remotest depths of space. What is their scientific importance? 1) A cosmic ray impact led to the discovery of the positive electron, a fundamental particle of matter. 2) The geographic distribution of the rays facilitates study of Earth's magnetic field. 3) For laboratory work cosmic rays provide atomic bullets thousands of times more powerful than any produced by man. 4) Their behavior at high voltages has already indicated a deficiency of electrodynamic theory which must be rectified. 5) Since about 30 pass through the human body every second, they may have some effect on life & death.

Controversy Closed. Dr. Millikan was among the packed throng which heard Dr. Compton last week in St. Louis. He did not rise, when the speaker had finished, to challenge his conclusions or even to ask a question. Impartial observers were therefore ready to write off their classic controversy as closed, to call it a cosmic clearance. If Dr. Millikan still cherishes the conviction that most of the cosmic rays are photons, he stands almost alone. Three years ago he remarked that if he ever wanted to change his mind, he hoped he would not be pilloried. He has not been pilloried.

Elephant Toes. When Arthur Compton was 10 he wrote a monograph on why some elephants are three-toed, others five-toed, explaining why he found his view at variance with that of other authorities. His mother concealed her amusement. When she recalled the incident with a smile many years later, her famed son replied: "Mother, if you had laughed at me then you would have killed my interest in research."

The family into which Arthur Compton was born 43 years ago in Wooster, Ohio, is something for students of heredity and environment to cluck over. The father is Elias Compton, Ph.D., D.D., Presbyterian clergyman, longtime professor of philosophy and psychology at the College of Wooster. The mother is Otelia Catherine Augspurger Compton, sprig of a German Mennonite family, who three years ago got an LL.D. for being "wife and mother of the Comptons." The parents did not try to choose careers for their four children but encouraged their natural bents. ''We used the Bible," said Father Elias, "and common sense."

Hardened by summers in the Michigan woods, the boys distinguished themselves in Wooster athletics. Karl kicked the longest field goal in Wooster history. He grew up to be president of Massachusetts Institute of Technology, chairman of President Roosevelt's Science Advisory Board, a burning advocate of Federal aid to science. In St. Louis last week, as incoming president of the A. A. A. S., he decried the AAA (see p. 12), urged that new industrial uses be found for agricultural products.

Wilson Martindale Compton, Ph.D., onetime professional baseballer. onetime economics professor at Dartmouth, is Washington contact man for the lumber industry.

Daughter Mary graduated from Wooster magna cum laude. The best the boys could do was cum laude. She is the wife of the administrative head of Allahabad University's Ewing Christian College (1,500 students) in India.

Compton Effect. In his teens Arthur built a glider that actually flew, published articles on aeronautics, made an astronomical clock for a telescope, took pictures of Halley's comet. He got his Ph.D. at Princeton with a dazzling record. After two years of industrial research on lamps for Westinghouse, he said to his wife, "Betty, I'm going back to university work." This was something of a gamble, but he landed a research fellowship at Cambridge under Lord Rutherford. He was appointed head of the physics department at Washington University (St. Louis), went from there to Chicago at the invitation of the late, great Albert Abraham Michelson.

His measurements of x-ray wave lengths convinced Compton that such rays, although a form of light, could act like bullets as well as waves. If on colliding with gas atoms they lost part of their energy as bullets, they should recoil as waves weaker in intensity and hence longer in wave length. In addition they should kick electrons out of the gas. With apparatus so sensitive that it measured one ten-millionth of the energy of a mosquito climbing an inch of screen, he showed that this was true. This "Compton effect" went far to explain photo-electricity and to make the old idea of a light-conducting ether, already in disrepute, even more unnecessary since light as bullets could travel indefinitely through empty space. The "Compton effect" won him a Nobel prize for physics in 1927.

With his wife and two sons. Dr. Compton lives in Chicago in a big brick house filled with souvenirs of their world tour. He does not know the taste of hard liquor, almost never smokes, always offers a cigaret to women visitors. He plays such a bang-up game of tennis that he sometimes has a hard time finding worthy opponents. Several times a month he puts in an evening of mandolin-playing with three friends. When his graduate students have finished an examination, he likes to dine them and take them to the theatre.

God & His Children. He has one class a day, at 8 a. m., after which he works in his office, which has a black steel desk, cream walls, tan curtains, grey rug, a cosmic-ray counter clicking away in a corner; or in the laboratories just outside where he has $50,000 worth of equipment for his own researches. He does much of his own experimental work, and his assistants admire his manual skill. He is reputed the best scientific glassblower in the Midwest.

A deacon in the Baptist Church, Dr. Compton attends nearly every Sunday, is actively interested in missions, Y. M. C. A. and settlement work. Like Britain's Eddington, he sees in Heisenberg's Uncertainty Principle (which avers that the behavior of electrons is unpredictable) evidence that man is not an automaton in a mechanistic universe, but a free agent responsible to his Creator. "Science can have no quarrel," says Arthur Compton. ''with a religion which postulates a God to whom men are as His children."

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