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Science: Cosmic Dispute

6 minute read

With an almost cosmic calm, two great U.S. physicists, both Nobel Prizemen, last week joined again in spirited dispute over the nature of cosmic rays. The scene of the controversy was the annual meeting of Washington’s National Academy of Sciences. It was not the first such dignified disagreement between devout, handsome Arthur Holly Compton, of the University of Chicago, and pious, white-crested Robert Andrews Millikan of California Institute of Technology. Several years ago Millikan reached the conclusion that cosmic rays consist of tiny, electrically neutral packets of radiation called photons. Compton insisted that they were electrically charged material particles. By 1936 most physicists judged that Compton was right. And Millikan agreed—for science is an even more sporting game than tennis.

Three big cosmic ray questions then remained to be answered: 1) The rays may be electrical particles, but are they electrons, positrons, protons,* or what? 2) From what parts of space do the rays shower upon the earth? 3) What events in space produce them and endow them with highly penetrating energies up to several hundred billion electron volts?

When the speeding particles of cosmic radiation hit the earth’s upper 5% of atmosphere, like billiard balls they pass their energy on to other particles knocked from the nuclei of atmospheric atoms. Hence cosmic radiation at sea level is of a secondary nature, consisting largely of mesotrons—particles intermediate in mass between electrons and protons. So up into high altitudes Physicist Compton sent his instruments to seek the nature—not the number, as earlier altitude studies had sought—of the primary rays.

Last week he reported that the primary particles 1) can penetrate as much as seven inches of lead, 2) do not set off showers of new particles when striking a lead plate. But electrons, physicists know for sure, can penetrate only four inches of lead and definitely produce secondary showers of lead particles. Concluded Physicist Compton: primary cosmic rays cannot be electrons, must consist almost solely of the heavier, more energized protons.

But unruffled Physicist Millikan insisted last week that the primary rays are mostly electrons. He then went much further. He announced, after some ten years of brooding and research, that cosmic rays result from the self-annihilation of atoms in interstellar space.

Certain nebulae in interstellar space seem to contain five elements—helium, carbon, nitrogen, oxygen and silicon—each of which is ten times as abundant as any other element except hydrogen. Experiments with atom-smashing machines and theoretical reckoning indicate that annihilation of a helium atom produces energy of 1.9 billion electron volts, of carbon 5.6, of nitrogen 6.6, of oxygen 7.5, of silicon 13.2.

The earth itself is a great spinning magnet which deflects incoming electrical particles in several ways. Only the strongest cosmic rays can penetrate the earth’s far-flung magnetic field at the magnetic equator, but even the weakest can get in near the magnetic poles. Thus a physicist traveling away from the magnetic equator should be able to detect one by one the appearance of new bands of cosmic energy as the earth’s resistance weakens. And these energy bands should correspond to the kinds of disintegrating atoms far off in space.

So Millikan, with his young, whip-smart colleagues Henry Victor Neher and William Hay ward Pickering, voyaged to India, through which the magnetic equator passes. The scientists’ hopes were fulfilled. At Bangalore in southern India, cosmic rays shot 500 to the minute through their instruments. This represented the 17 billion electron volt debris of such heavy atoms as iron and chlorine. At Agra in central India, the 17 to 14 billion electron volt zone, there was little radiation increase—but this was expected, since elements which might produce such voltages are rare on earth and in space. At Peshawar, near Khyber Pass, radiation increased 21%. This was the predicted appearance of the 13 billion electron volt particles from disintegrating silicon.

Millikan did not pursue cosmic rays through Kazakstan and Siberia, instead substituted the same magnetic latitudes in the U.S. In Texas the six billion electron volt carbon rays began coming through, in Nebraska the four and five billion electron volt rays of beryllium and boron, in North Dakota the two billion electron volt rays of helium.

Why the interstellar atoms curiously annihilate themselves, Millikan has no idea. William Francis Gray Swann of the Bartol Institute at Swarthmore, Pa. pooh-poohs the theory by ironically suggesting atomic boredom or loneliness. But Millikan’s co-workers shrug their shoulders like detectives who have not found a motive but are sure they have evidence of crime. The bigger question is: whose evidence is right? Compton’s, that cosmic rays are protons? Millikan’s, that cosmic rays are electrons?

Among other disclosures at the National Academy meeting were two huge contributions to genetics, the science of heredity:

Genes & Viruses. At the Cold Spring Harbor, L.I. laboratory of the Carnegie Institution, Geneticists Albert Francis Blakeslee and Amos Geer Avery have zealously raised acres of Jimson weed. By careful breeding they produced plants with narrow leaves, spineless fruit capsules, petals instead of tubular flowers—the same characteristics that Jimson weed has when attacked by virus disease. This, according to Dr. Blakeslee, bears out the idea that there is a kinship between genes—the protein molecules in the nuclei of cells which determine inherited characteristics—and viruses—the self-reproducing protein molecules which cause many diseases of man, animals, plants (TIME, May 5).

The major difference seems to be that genes are locked within the nuclei of cells, where their influence is controlled to a specific end, but viruses are free to proliferate uncontrolled. It is thus possible, speculated Dr. Blakeslee cautiously, that virus diseases—and perhaps even cancer—may sometimes be caused by genes which have escaped the cellular discipline and become viruses.

Motherless Frogs. Five years ago Physiologist Gregory Goodwin Pincus of Clark University produced fatherless rabbits by removing ova from virgin females, fertilizing the ova with a salt solution, replanting the fertilized eggs in other females to gestate (TIME, April 6, 1936). Last week Dr. Keith Roberts Porter of the Rockefeller Institute announced that he had produced a greater wonder: motherless tadpoles. He removed the nucleus from a frog’s egg at the moment of fertilization, but before it could unite with the nucleus of the male sperm. This made the mother’s contribution apparently a mere anonymous drop of protoplasm with no inheritable characteristics, while the sperm alone contributed a share of genes.

The egg not only produced a tadpole, but a tadpole which showed some characteristics of its mother. The obvious and significant conclusion: The intricate mechanism of embryonic development is not determined by genes alone, as most geneticists have thought, but depends on the whole protoplasm of the egg cell.

*Scientists do not try to visualize the atom; its mechanics are too complex, too alien to the familiar things of life. Laymen can visualize it after a fashion by imagining a heavy nucleus composed of protons and neutrons clumped together sur rounded by a sort of throbbing mist of electrons.

Positrons are created in free space by atomic collisions.

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