COSMIC RAYS

Evening Star, Issue 21090, 30 April 1932, Page 12

COSMIC RAYS

WORLD-WIDE RESEARCH PROFESSOR COMPTON'S LECTURE At the University last evening a largo audience listened with great interest to Professor Arthur H. Compton’s lecture on cosmic rays. Professor Jack, who was in the chair, pointed out how they were honoured to nave a visit from such a distinguished physicist as Professor Compton. The American scientist was also welcomed by Sir Thomas Sidey (Chancellor of the Otago University), who stated that during the last few years the people of New Zealand had been brought more closely into touch with the work of the American universities than formerly. One common ground on which all universities were united was as regards the search for truth and the efforts to extend the sum of human knowledge. In his opening remarks Professor Compton said that the discovery of cosmic rays had followed the discovery of X-rays and radio activity, and it would probably take generations to discover whether man could control this vast energy to his own advantage. It was not known yet what cosmic rays actually were; nor was it known precisely where they came from. Nevertheless, there were certain phenomena they had observed which it was possible to name as cosmic rays, and their problem now was just to find out what they were and where they came from. It had been shown by experiments that there was an ionising agent in the air above the mountains, and the name most in common use for this agent was cosmic rays.

Tho lecturer said that it had been found that air, which was normally a conductor of electricity to a very small extent, became a very much better conductor in tho presence of X-rays or radio-active rays. It had been found by experiments in balloons that the conductivity of the air decreased up to a height of about 1,000 metres, at which level the gamma-rays from radioactive substances in the earth ceased to have any effect. Above 1,000 metres the conductivity increased until at ten miles it was 100 times as great as at sea level. This great height had been reached about a year ago by the intrepid Belgian, Professor Picard, who had ascended in a. metal sphere attached to a balloon. It was inferred that the upper atmosphere must be pervaded by other rays much more penetrating than the gamma-rays of radio-activity. Experiments conducted by Dr R. A. Millikan in the water of mountain lakes showed that these rays, now known as cosmic rays, were five to fifty times as penetrative as gamma-rays. Millikan’s theory was that they were electro-mag-netic rays, but probably having onefiftieth of the wave-length of gammarays, to which the description electromagnetic also applied, as it did to light and heat waves and wireless waves. He also held that cosmic rays were generated by the formation of hydrogen atoms in interstellar space and by the coalescence of hydrogen atoms there to form atoms of helium, oxygen, and other heavier elements. Sir James Jeans, on the other hand, had put forward a theory that the rays were generated by the dissolution of hydrogen atoms in space. Both theories were based on the hypothesis that the rays were electro-magnetic. Another theory was that cosmic rays were of the same nature as beta-rays, namely, streams of electrons or particles of negative electricity. Whatever their nature, the energy associated with them was tremendous—up to 10,000 times as great as that associated with radio-active processes. If the rays originated in space they were of great cosmic significance. On the other hand, they might possibly originate only in the upper atmosphere. The lecturer said that so far some interesting things had been discovered, It appeared that the cosmic rays near the Equator were of less intensity than was the case at the Poles. The investigators were really on an exploring expedition, trying to open up new territory. Of course, it might be found that if they eventually did find the source of the power of cosmic rays, it would be in some inaccessible point and bo of no practical value. It would appear, concluded the lecturer, that the energy must be concerned with the nucleus of the atom.

Professor Compton was accorded a hearty vote of thanks for his address.