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The use of the orthographic projection in crystallography

Published online by Cambridge University Press:  14 March 2018

Harold Hilton
Harold Hilton*
Affiliation:
Bedford College (University of London)
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Extract

The geometrical representation of the faces and edges of a crystal is obtained (i) by drawing lines through a fixed point O perpendicular to each crystal-face meeting a fixed sphere with centre O in a point (face-pole) representing that face, (ii) by drawing lines through O parallel to each crystal-edge meeting the sphere in a point (edge-pole) representing that edge. This representation is inconvenient as being in three dimensions, and therefore it is customary to map the sphere on a plane. This is usually done by means of the stereographic or gnomonic projection.

Type
Research Article
Information
Mineralogical magazine and journal of the Mineralogical Society , Volume 18 , Issue 84 , June 1917 , pp. 122 - 129
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 1917

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References

page 122 note 1 We denote the projections of p, q,… by P, Q,… throughout. If P lies on the fundamental circle, p coincides with P.

page 124 note 1 It comes to the same, if we suppose the sphere kept fixed and π altered.

page 125 note 1 e. g. , if θ-tan-11/3 = 26', φ = 9°28', then COK = 27° 48', ε=1° 32', ψ=20°38'. These values are taken in fig. 2.

page 126 note 1 o is tile point on the sphere whose projection is O, so that oO is perpendicular to Π.