File:X rays and crystal structure (1915) (14755056676).jpg

Identifier: xrayscrystalstru00braguoft (find matches)
Title: X rays and crystal structure
Year: 1915 (1910s)
Authors: Bragg, William Henry, Sir, 1862-1942 Bragg, William Lawrence, Sir, 1890-1971
Subjects: Crystallography X-rays
Publisher: London : G. Bell
Contributing Library: Gerstein - University of Toronto
Digitizing Sponsor: MSN

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Text Appearing Before Image:
, fourfold axes of symmetry, and acentre of symmetry. A consideration of the structure in Fig. 45 showsthat there are no reflection planes of symmetry or
Text Appearing After Image:
Fig. 45. rotation axes of symmetry which could give rise tothe holohedral symmetry of the crystal as a whole.Their places are taken by glide planes of symmetryand screw axes of symmetry. Two of the fourfoldscrew axes are marked in Fig. 45 ; it will be seen how 148 CRYSTAL SYMMETRY AND THE the points 12 3 4 are arranged in a spiral roundthe axis. The dotted line represents a plane ofgliding reflection. By its operation 1 turns into2 and 3 into 4. 1 is to be imagined reflected inthe plane, at the same time receiving a translationwhich brings it to 2. If the structure has as elements of symmetry thesescrew axes and gliding planes, the crystal must havecorresponding rotation axes and planes of symmetry.A rotation axis is, of course, the only kind which canbe possessed by a crystal, for when the crystal is imagined turned round this axis throup^h 2 into^ ^ n self-coincidence, its centre must remain fixed. The diamond crystal, according to the structure here put forward, is holohedral. Ther

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