40 WRIGHT: A NEW CRYSTAL-GRINDING GONIOMETER 



mounted so that it can be rotated about a horizontal axis (fig. 

 3c). ^ The different possible lens combinations are: (A) For 

 mewing crystal surfaces: (1) Objective alone; (2) objective 

 P+ objective 0+ eyepiece E. (B) For viewing reflection signals: 

 (1) Objective 0+ eyepiece E; (2) objective P-\- objective 0. 



SYSTEMATIC ADJUSTMENT 



(a) Adjustment of telescope. (Fig. 3a) 



(1) Use lens combination Bl. Illuminate reflecting edge of cover 

 glass prism at H (fig. 3a) and center same by placing a flat glass plate 

 on telescope-mount above prism X and then bringing reflected image of 

 edge to coincidence with edge itself. 



(2) Mount reflecting glass plate (fig. 3c) in S (fig. 2) so that edge of 

 plate is normal to axis D D. Adjust telescope axis normal to axis D D 

 by means of adjustment screws K and / and test adjustment by noting 

 that the image obtained by reflection from either side of the glass plate 

 coincides with the reflecting cover-glass edge. This is accomplished 

 by rotating the glas? plate about the horizontal axis D D. 



(3) Center telescope by means of eccentric stop screw at H. 



(4) Center and adjust in similar manner the reducing attachment 

 P to the positions just obtained. Use adjustment screws, Q, R, S for 

 the purpose, 



(b) Adjustment of axis P S 



(1) Adjust axis P S (fig. 2) normal to axis D D by means of mounted 

 glass plate (fig. 3c) so turned that its reflecting surface is normal to axis 

 P S. Axis is adjusted when signal observed in telescope (lens combina- 

 tion J51) remains stationary during rotation of glass plate about axis P 

 and coincides with reflecting edge of cover-glass prism. Adjustment 

 screws are Ki, K^ in conjunction with wedge shaped, hardened steel bar 

 / which is moved forward by means of the flanged screw /. 



The tilting is done on the steel axis at p. (2) Center axis P S 

 to intersection of axis D D by means of minute glass bead mounted on 

 pin inserted in *S (flg. 2). Use lens combination Al. When properly 

 centered by means of eccentric fitting on axis D D (clamped by screw 

 d, fig. 2) the centered glass bead remains stationary on rotation about 

 axis D D or axis P S. 



(c) Adjustment of grinding plate 



(1) Adjust grinding plate T normal to axis of rotation W by means 

 of screws y, figure 2. Adjustment is attained when a distant object, as 

 seen by reflection from the top surface of the plate, remains stationary 

 on rotation of the plate about axis W. In case the surface of the tin 

 grinding disk does not reflect light adequately, an optically plane-paral- 

 lel glass plate, 3 inches in diameter, is placed on top of the grinding 

 disk and furnishes a satisfactory reflection of the distant object. 



6 Goldschmidt, V., Zeitschr. Krist., 29: 342. 1898. 



