(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. Göckel 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.