THE ATOMIC THEORY.

Hawera Star, Volume XLV, 11 May 1925, Page 7

THE ATOMIC THEORY.

RESULT OF TWENTY YEAR’S RESEARCH. SIR E. RUTHERFORD’S STATEMENT. •In liis latest lecture series on “The Counting of the Atoms,” delivered before the Royal Institution, Sir Ernest Rutherford showed how with a knowledge of elementary arithmetic and a- slight amount of experimental skill any observer could watch the effects produced by the single atoms shot out from a speck of radium. Another passage in which he attempted to bring the individual atom within the scope of the noil-technical man. described how to-day it would be quite possible to make use of one of the particles of radium to set machinery in motion, though he added that he did not recommend the construction of such a machine as an economic proposition.

It was. he said, the alpha particle of radium, which composed of an atom of helium carrying, not one, but two charges of positive electricity, which first provided a method of detecting a single atom of matter. It possessed a charge or two of electrical units and a mass of four, and was shot out with such energy that the individual .pan-tide could be detected in a number of ways. It produced, for instance, a visib’e flash of light, or scintillation, in striking a crystal of phosphorescent zinc sulphide, and a visible effect on a photographic plate. The entrance of an alpha particle into a vessel could be readily detected by e'eetric methods, and the actual number expelled per second by a gram of radium, about 150,000 millions, had been counted. COUNTING THE ATOMS

Since the helium produced by indium, which was due to the accumulated alpha particles, could be measured it was possible to determine the actual number of alpha particles required to produce a cubic centimetre of helium gas. Tlie method of counting the atoms was very simple and direct, and afforded convincing evidence of the correctness of the various indirect methods of finding the number and mass of the atoms. By means of an electric valve and a relay it- was possib’e to arrange that a lamp should be lighted every time that an alpha particle or a swift electron entered the receiving vessel. More than 12 years ago he had succeeded iii obtaining approximate valves of tlie size and mass of the atom, and these agreed very closely with those obtained by the highly refined water drop method used by Professor Millikan. “I never cease to wonder.’” he continued, “that in those early experiments 1 obtained figures so close to what are now known to be correct. Tlie researches during the past 20 years have given a. complete verification of the atomic theory of matter, and supplied us with a variety of methods not only for determining the weight and number of tlie atoms, but also for detecting individual atoms under special conditions.”