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A Three-Circle Goniometer

Published online by Cambridge University Press:  14 March 2018

G. F. Herbert Smith
G. F. Herbert Smith*
Affiliation:
Mineral Department of the British Museum
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Extract

The object of goniometrical measurement is to determine in the simplest and quickest manner possible the geometrical constants of crystals and the indices of their faces. The ideal instrument should enable the observations to he conveniently and quickly made, and present them in such a form that the indices of the faces may be easily calculated. It is claimed for the tbrm of goniometer described in this paper that it does approximate to such an instrument. Before entering into the description it will not be out of place to discuss briefly the two types at present in existence, and point out their advantages and disadvantages.

Type
Research Article
Information
Mineralogical magazine and journal of the Mineralogical Society , Volume 12 , Issue 56 , October 1899 , pp. 175 - 182
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 1899

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References

page note 1 Proc. Camb. Phil. Soc., 1882, IV, 236. Abstract in Zeits. Kryst. Min. 1883, VII, 619.

page note 2 Zeits. Kryst. Min. 1893, XXI, 210.

page note 3 Zeits. für Instrumentenk., 1893, 1.

page note 4 Zeits Kryst. Min. 1893, XXI, 574.

page note 5 XXVI, 458. Abstract in French in Bioliothèque géologique de la Russie, 1890, VI, 97

page note 1 loc. cit.

page note 2 Cf. the very suggestive remarks by Signor C. Viola, Zeits. Kryst. Min., 1898, XXX, 423:--

"Ich bin der Meinung, dass, sowohl was die Messung der Krystalle, sis such was die Signatur der Flächen anbetrifft, man hauptsächlieh auf die Zonen Riickaicht haben muss, denn nur dadurch kann eine Erleichterung herbeigeführt werden, obwohl die moisten Fliichen yon den Zonen ein wenig abweichen.

"Das Princip der Zonen, odor was gleich ist, das Princip tier Rstionalität darf nicht bei Seite gelassen werden, wiewohl es in tier Natur nioht mit absoluter Strenge zutrifft. Ein solehes Princip ist eben der Leitfaden der Krystalle, wie das Newton'sche Gesetz, das such nicht genau in der Natur gilt, fiir die Bahnberech. hung der Plaoeten jedoch das Fundament bildct.

"Erfüllt ein Theodolithgoniometer solche Bedingungen nieht, so h:tt es besscren Instrumenten Platz zu machen."

page note 1 Throughout this paper reference will be made Lo the circles by these letters.

page note 2 The intersection of the axes of the telescope and collimator.

page note 3 Vide Fedorow, lee. cit.

page note 1 The latter adiustment may be employed to make the reading of B a convenient quantity when the axis of c is vertical.

page note 2 That this angle could not be conveniently made larger is one of the disadvantages of adapting an existing goniometer. It might, however, in an instrument entirely new from the beginning be easily arranged that B could be turned round the axis of A through nearly 300%

If the axis of c be vertical, this zone may be measured whatever be the reading of A, but it is only when the latter reads 0°0 that the reading of c for any particular face indicates the position in which it is parallel to B.

page note 2 The zone whose edge is parallel to the axis of c.