New pathways in science / by Sir Arthur Eddington.

  • Eddington, Arthur Stanley, Sir, 1882-1944.
Date:
1935
Catalogue details

Licence: In copyright

Credit: New pathways in science / by Sir Arthur Eddington. Source: Wellcome Collection.

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    backwards, chlorine (17) has 7 electrons in its M group; these are as restive and dissatisfied as a party of 7 bridge- players. It would be an admirable arrangement for both sides if chlorine could borrow sodium’s lonely electron to complete its group. The arrangement can be made, and the two atoms combine to form a molecule of common salt (NaCl). Besides matter, which we dissect into protons and electrons, the other chief performer in the drama of physics is radiation. Radiation is the general name given to electromagnetic waves, or waves in the aether which is the continuous back¬ ground between the protons and electrons. These waves may be of any length (from crest to crest) or equivalently of any frequency or pitch. One particular octave can stimulate our optic nerves, and within this range of frequency the electro¬ magnetic waves constitute light. Other ranges of frequency have other characteristic manifestations. Arranged in order of diminishing wave-length and increasing frequency, the waves are classified roughly as Hertzian or broadcasting waves, infra-red or heat rays, hght, ultra-violet or photo¬ graphic rays, X rays, y rays. If the primary cosmic rays are electromagnetic waves they are of still higher frequency than the y rays, but it now seems more probable that they are high-speed particles. We shall now consider briefly how atoms and radiation interact with one another. When there is energy straying round in the form of radiation, or when the atoms are jostling one another with energy derived from their high temperature, the satellite electrons will not necessarily occupy the orbits which correspond to minimum energy. The atom is then said to be “excited”. But the atom cannot take up just any quantity of energy; the amount has to be that which will hft an electron from one orbit to another vacant orbit. Thus for each atom there are a number of characteristic amounts of energy which correspond to the different possible transi-