

280 



O. Polciche — Crystal Measurement^ etc. 



an illustration. Its construction is best explained bj reference 

 to the outline view and plan, figs. 2 and 3. H is the horizontal 

 circle revolving about the axis A, graduated and provided with 

 fine adjustment and vernier. Eigidly attached to H by an 

 arm and at right angles to it is the vertical circle Y revolving 

 about the axis v and also graduated and provided with fine 

 adjustment. The axis -y supports an adjusting device such as 

 is found on the ordinary goniometer and upon it the crystal is 

 mounted by means of a carrier m capable of independent 

 adjustment.* 



The collimator C and telescope F are horizontal ; they may 

 be moved relative to each other and the angle between them 

 measured. 



By revolution of Y (from an arbitrary zero through an 

 angle <^) each face of the crystal may be brought perpendicu- 

 lar to H. By revolution of H (through angle p from arbitrary 

 zero) the face may be brought perpendicular to S, the bisectrix 

 of the angle C^F, also and will then reflect the signal upon the 

 crosshairs of the telescope. The angles ^ and /o, read upon 

 the vertical and horizontal verniers respectively, determine the 



principle and a similar construction are employed in the Universal-(TheodoHth-) 

 goniometer (Zeitschr. f. Kryst., xxi, 1893, p. 514) devised by Fedorof and con- 

 structed by Fuess of Berlin and the instrument of Czapski (Zeitschr. f. Instru- 

 mentenkunde, 1893, i) is also similar. 



* See description of this convenient device (Krysttallrager) in Zeitschr. f. Kryst., 

 XX, 1892, p. 344; idem xxv, 1896, p. 541. 



