Abstract
UNTIL very recent years, the addresses of presidents of Sections of the British Association were never made subjects of formal discussion. The address delivered on Monday, August 11, by Sir William Bragg to Section A (Mathematical and Physical Science) of the British Association meeting at Toronto departed from the former custom in being an introduction to a joint discussion with Section? (Chemistry), on crystal structure. Sir William Bragg explained how X-rays have made it possible to analyse the structure of crystals, thus opening up the chemistry of the solid. The X-rays tell us the number of molecules in the crystal unit and the mode of their arrangement, on which, of course, many properties of the substance depend. It may be noted that just as there are atoms of silicon and of oxygen, and a molecule of silicon dioxide, so there is a crystal unit of quartz consisting of three molecules of silicon dioxide arranged in a particular way. There are thirty-two classes of crystals, according to the kind of external symmetry which they display; but now that he can look into the interior of the crystal, Sir William Bragg finds that there are 230 different modes of internal arrangement. This is a new kind of crystal-gazing.
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Crystals and Cells. Nature 114, 233–235 (1924). https://doi.org/10.1038/114233a0
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DOI: https://doi.org/10.1038/114233a0