1895.J Cutting, Grinding, and Polishing Section-plates, $c. 325 



Instrument for Cutting, Grinding, and Polishing Section-plates and Prisms of 

 Mineral or other Crystals. 



and its centering (Z>) and adjusting (c) movements, are similar in prin- 

 ciple to the corresponding arrangements in the smaller instrument, 

 although many details are altered for the sake of greater rigidity. 

 The same likewise applies to the goniometrical telescope d and colli- 

 mator e and their mode of support. 



The crystal holders, in addition to being provided with cross- 

 grooved surfaces for the reception of the cementing wax, which 

 should be the hardest variety used by opticians, are further pro- 

 vided with protecting rims, so that the wax is firmly held in a 

 shallow cup. Three ordinary holders are supplied, of T 5 , f, and 

 |- in. diameter respectively. Two holders, of ~ and -J- in. 

 diameter, are also furnished, which permit of a certain amount of 

 rotation of the crystal after fixation of the holder in its socket, as 

 described in the former communication, and one of which is shown 

 in position at / in the illustration. Also there is the special 

 holder for use in grinding a second surface parallel to the one first 

 prepared, and it is provided with two lower caps pierced by apertures 

 of T 9 and T 5 -g- in. respectively, together with a dozen glass discs 

 ground to fit each. 



The grinding apparatus resembles that of the smaller instrument, 



