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An improved form of petrological microscope: with some general notes on the illumination of microscopic objects

Published online by Cambridge University Press:  14 March 2018

G. W. Grabham
G. W. Grabham*
Affiliation:
Sudan Government
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Extract

It is more than twenty-one years since Mr. Allan B. Dick communicated a description of the microscope, now generally associated with his name, to this Society. The instrument is familiar to all mineralogists, and it will suffice to say that the main feature consisted in having the polarizing and analysing prisms arranged so that they can be rotated simultaneously, instead of turning the object on the stage between them. The rotating stage is never very satisfactory, especially when it is desired to examine minute crystals in convergent light. In two pamphlets, published later, Mr. Dick extended his description of the instrument and gave some methods of using it.

Type
Research Article
Information
Mineralogical magazine and journal of the Mineralogical Society , Volume 15 , Issue 72 , September 1910 , pp. 335 - 349
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 1910

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References

Page 335 note 1 Dick, A. B., ‘A new form of microscope.’ Mineralogical Magazine, 1889, vol. viii, pp. 160–163 CrossRefGoogle Scholar.

Page 335 note 2 A. B. Dick, ‘Notes on a new form of polarizing microscope,’ London (J. Swift & Son), 1890. ‘Additional notes on the polarizing microscope,’ London (J. Swift & Son), 1894.

Page 336 note 1 A. B. Dick, ‘Additional notes,’ (1894), preface.

Page 337 note 1 The block for this figure has been kindly lent by Dr. A. E. H. Tutton, F.R.S., with the permission of Messrs. Macmillan & Co., Ltd., the publishers of his forthcoming book on crystallography.

Page 338 note 1 The matter, however, is referred to both by E. Weinschenk in his ‘Anleitung zum Gebrauch des Polarisationsmikroskops’ (2nd edit., Freiburg i. B., 1906), and by H. Rosenbusch and E. A. Wiilfing in their ‘Mikroskopisehe Physiographie der petrographisch wichtigen Mineralien’ (Stuttgart, 1904).

Page 339 note 1 The following quotation from Dr. E. J. Spitta's excellent book, ‘Microscopy,’ London, 1907, p. 177, will serve as an example : ‘For example, bacteriologists seem mostly agreed that the bacillus tuberculosis is probably not an organism likely to have a capsule under ordinary conditions, and yet with a narrow cone, whether the specimen be stained or unstained, a very pronounced encircling capsule, as bright and clear as possible to the eye, appears in every case ; yet, as the cone is steadily and slowly increased, so does this mysterious capsule disappear.’ To the mineralogist, familiar with Becke's white-line effect, such a phenomenon offers no difficulty, and indeed is often sought for as a means of diagnosis. It is clear, however, from the sections dealing with polarized light that our author is not very familiar with the use of the microscope in petrology.

Page 341 note 1 Rosenbusch, H. and Wülfing, E. A., ‘Mikroskopische Physiographic der petrographisch wiehtigen Mineralien,’ Stuttgart, 1904, vol. i, pt. 1, p. 263 Google Scholar. I have not been able to refer fully to the original papers, but a full account of them appears to be given in this textbook, which includes references to the work of other authors bearing on the white-line effect, notably W. Salomon and C. Viola.

Page 346 note 1 H. Rosenbusch and E. A. Wülfing, loc. cit., p. 266.