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A method of determining the angular direction represented by a point in the directions-image of an object under the microscope

Published online by Cambridge University Press:  14 March 2018

John William Evans
John William Evans*
Affiliation:
Imperial College of Science and Technology, and Birkbeck College
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Extract

The determination of the direction in which the light illuminating a point in a directions-image (the so-called image in convergent light) was travelling when it reached the objective has hitherto been carried out by first measuring the position of the point in the image and thence calculating the angular direction it represents. It is usually assumed that the distance of a point in the image from the centre of the field is in proportion to the sine of the angle between the path of the light that illuminates the point and the axis of the microscope.

Type
Research Article
Information
Mineralogical magazine and journal of the Mineralogical Society , Volume 18 , Issue 83 , November 1916 , pp. 52 - 57
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 1916

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References

page 52 note 1 Becke, F., Min. Petr. Mitt., 1895, vol. xiv, pp. 568–565 Google Scholar.

page 53 note 1 Wright, F. E., Amer. Journ. Sci., 1907, vol. xxiv, pp. 886–887 Google Scholar; ibid., 1910, vol. xxix, p. 428 ; Journ. Wash. Acad. Sci., 1911, vol. i, pp. 60-61 ; Min. Petr. Mitt., 1908, vol. xxvii, pp. 298-800.

page 53 note 2 Beeke, F., Min, Petr. Mitt., 1894, vol. xiv, pp. 376–378 Google Scholar.

page 53 note 3 Lenk, H., Zeits. Kryst. Min., 1896, vol. xxv, pp. 379–380 Google Scholar.

page 53 note 4 Sommarfeldt, E., Zeita wisa Mikr., 1905, vol. xxii, pp. 356–362 Google Scholar.

page 53 note 5 F. E. Wright, ' The Methods of Petrographic-Microscopic Research.' Carnegie Institution, Washington, 1911, pp. 174-175.

page 54 note 1 A plate with a similar arrangement of concentric lines appears to have been employed as an apertometer by W. Volkmann (Aus Theorie und Praxia des Mikroskopes, Berichte fiber Appar. u. Anlag. yon Leppin & Mascbe, Berlin, 1911, vol. viii, p. 5, noticed by E. A. Wiilfing, Fortschritte in Krist. Pet,, 1913, vol. iii, pp. 71, 78), but I have not been able to see the original description.